CN111093967A

CN111093967A - Optical structure providing a bicolor effect

Info

Publication number: CN111093967A
Application number: CN201880059394.4A
Authority: CN
Inventors: R·W·菲利普斯; C·C·里奇; J·M·彼得森
Original assignee: Wavefront Technology Inc
Current assignee: Wavefront Technology Inc
Priority date: 2017-10-05
Filing date: 2018-08-03
Publication date: 2020-05-01
Also published as: WO2019070335A1; EP3648967B1; EP3648967A1; CA3072286A1; TW201922475A; RU2020105931A; BR112020003100A2; US20210271094A1; US11675203B2; US10838218B2; EP3648967A4; US20190107726A1

Abstract

A document, product or package (e.g. banknote, passport or the like) includes a structure having a two-color effect that changes color with viewing angle in both transmission and reflection. Such structures may be used as security features against the ability to effectively use counterfeit documents, products, packaging, and the like.

Description

Optical structure providing a bicolor effect

Incorporation by reference of any priority application

This application claims priority to U.S. provisional application No. 62/568,711, filed on 2017, 10/05/h, the entire disclosure of which is expressly incorporated herein by reference.

Statement regarding federally sponsored research and development

The invention was made with government support under contract number TEPS 16-34769 awarded by the U.S. engraving and printing office. The united states government has certain rights in this invention.

Technical Field

The present invention generally relates to thin interference optical structures, films, coatings, and pigments for producing color in both reflective and transmissive modes. More particularly, these structures, films, coatings, and pigments exhibit large color shift properties, where both reflection and transmission may change with changes in angle of incidence or viewing angle.

Background

The color shifting features can be used as a security device (e.g., on a banknote) to prevent counterfeiting. The color-shifting effect produced by the color-shifting material can be readily observed by an average person. However, the color shift effect produced by the color shift feature may be impractical for reconstruction using counterfeit copies produced by color copiers, printers, and/or photographic equipment. Color copiers, printers, and/or photography equipment use pigments based on dyes that are absorptive and thus the printed color may be insensitive to viewing angle variations. Thus, a difference between a real document including a color shift feature and a dummy document can be detected by tilting the document to see whether there is a color shift. Some color shift features that are available are opaque and exhibit color shifts for the reflective mode. In addition, counterfeiters have developed complex methods of compromising the effectiveness of existing reflective color shifting features as security protection. Thus, with respect to security devices, there is a need for new security features that are difficult to counterfeit and that can be easily incorporated into items such as banknotes.

Disclosure of Invention

A wide variety of structures including some at least partially transmissive optical structures are disclosed and contemplated by the present application. Advantageously, the change in these at least partially transmissive optical structures may exhibit a color shift relative to the viewing angle in both the reflective mode and the transmissive mode. Furthermore, variations of these at least partially transmissive optical structures may be integrated with documents (e.g., banknotes), packaging, and potentially other items, for example, to enhance security and/or prevent counterfeiting. Although such a feature described herein may be used in security applications (e.g., to reduce the incidence of counterfeiting), alternatively or additionally, such a feature may be used to provide an aesthetic effect or used for other reasons.

This application contemplates documents, products, and packaging having features that provide optical effects that change color with viewing angle in both reflection and transmission, such as security features. Color shifting relative to viewing angle in both reflection and transmission can be achieved by incorporating an at least partially transmissive optical structure as a security feature in a document, product, package, or the like. The at least partially transmissive optical structure may be a dichroic structure. The at least partially transmissive optical structure may be in the form of a thin film coating on a flexible support or substrate layer, such as a sheet, web, or carrier. In some embodiments, the at least partially transmissive optical structure comprises a pigment. In some cases, a collection of particles comprising at least partially transmissive optical structures may be contained in a medium and form, for example, an ink. Optical effects from the collection of particles can provide color shifts in reflection and transmission. The colors in transmission may be complementary to the colors perceived in the reflective mode. In some such embodiments, each particle may comprise the same structure or a similar structure.

Some implementations of at least partially transmissive optical structures contemplated herein may include at least two metal layers sandwiching at least one transparent layer therebetween. The at least one transparent layer interposed between the at least two metal layers may have a refractive index greater than, less than, or equal to 1.65. The at least partially transmissive optical structure contemplated herein may further comprise a transparent layer on the other side of the at least two metal layers. The transparent layer on a side of the at least two metal layers opposite to a side facing the sandwiched at least one transparent layer may have a refractive index greater than or equal to 1.65. The at least two metal layers may include a metal having a ratio of its (n) index of refraction to its imaginary (k) index of refraction less than 1.0. Thus, the metal of the at least two metal layers may have a ratio n/k smaller than 1. Without loss of generality, the real part n is the refractive index and indicates the phase rate, while the imaginary part k is called the extinction coefficient and can be related to the absorption. The at least two metal layers may comprise silver, silver alloys, aluminum, gold, and other metals or materials or combinations thereof.

Various optical structures contemplated in the present application can provide a color shift that varies depending on the viewing angle when viewed in both reflective and transmissive modes. Thus, these structures may be incorporated as security features for documents (e.g., banknotes or other documents) to verify the authenticity of the document. The structures contemplated in the present application may be configured for use as security threads (security threads), as laminates, as hot embossing, as window stickers, or as paint. A ply comprising a substrate (e.g. PET), a bi-color film and a protective UV curable resin may be adhered to the banknote using an adhesive as a unit. The structures contemplated in the present application may be configured for use in printing inks. Non-shifting transparent dyes or pigments can be incorporated with the optical structures contemplated in the present application to obtain new colors when viewed in both reflective and transmissive modes. It is further contemplated that two or more at least partially transmissive optical structures may be disposed over (e.g., printed or laminated over) each other to create unique color effects. An at least partially transmissive optical structure as contemplated herein may be configured or arranged to form, include, or otherwise display text, symbols, numbers, or figures that appear and/or disappear in reflection or transmission as the viewing angle of the security device changes. In other configurations, the figures, images, numbers, pictures, or symbols may be viewed at substantially all angles in transmission. For example, if a figure, image, number, picture or symbol is printed in black, it can be viewed in transmission at substantially all angles. In some cases, for example, text, numbers, pictures, or symbols can be underprinted and/or overprinted under and/or over the at least partially transmissive optical structure using existing printing techniques.

The at least partially transmissive optical structure may be included in or on or configured as a film, foil, coating, pigment or ink. When configured toIn the case of pigments, in some embodiments, the pigment may be encapsulated with a protective layer. The protective layer may comprise SiO₂. The protective layer may comprise a solution prepared using sol-gel techniques, such as an acid or base catalyzed tetraethyl orthosilicate (TEOS) reaction for increased durability. In some cases, the protective layer may further include silicon dioxide spheres having the same or different sizes. The silane coupling agent may be used in combination with a silane coupling agent including Silica (SiO)₂) The protective layer of (2) is bonded. The silane coupling agent may be bound to a resin, ink or coating vehicle. The resin, ink, or coating vehicle may comprise materials such as, for example, melamine acrylates, urethanes, polyesters, vinyl resins, acrylates, methacrylates, ABS resins, epoxy resins, styrene, and alkyd-based formulations, and combinations or mixtures thereof. In some implementations, an at least partially transmissive optical structure can be encapsulated, for example, with an encapsulation layer having an index of refraction that matches or closely matches the index of refraction of the article to which it is applied. In certain embodiments, the encapsulation layer may include a rough surface such that the particles do not tend to stick together or to the printing roll. The encapsulation layer may include a UV curable polymer.

These and other aspects of the at least partially transmissive optical structure will be apparent from the drawings hereof and from the description.

The at least partially transmissive optical structures disclosed herein may be used for security features included in documents, products, packaging, etc., in particular, as security threads in banknotes or as laminating strips, or as patches or as windows. Other items, such as passports, ID cards, chip cards, credit cards, stock or other investment securities, vouchers, admission tickets, and commercial packages that protect items of value, such as CDs, medical drugs, automobile and aircraft parts, etc., may also be protected from counterfeiting using the concepts and embodiments described herein. Furthermore, the at least partially transmissive optical structures disclosed herein may also be used in non-security applications.

While some optical structures discussed herein can provide color shift with viewing angle, optical structures that do not exhibit color shift with viewing angle or that produce very little color shift with viewing angle are also contemplated.

The systems, methods, and devices disclosed herein each have several inventive aspects, no single one of which is solely responsible for the desirable attributes disclosed herein. Various example systems and methods are provided below.

Example 1: an optical structure, comprising:

a first transparent dielectric layer having a refractive index greater than or equal to 1.65;

a first metal layer disposed over the first transparent dielectric layer, the first metal layer having a first refractive index, wherein a ratio of a real part (n) of the first refractive index to an imaginary part (k) of the first refractive index (k) is greater than or equal to 0.01 and less than or equal to 0.5;

a second transparent dielectric layer disposed over the first metal layer;

a second metal layer disposed over the second transparent dielectric layer, the second metal layer having a second refractive index, wherein a ratio of a real part (n) of the second refractive index to an imaginary part (k) of the second refractive index is greater than or equal to 0.01 and less than or equal to 0.5; and

a third transparent dielectric layer disposed over the second metal layer, the third transparent dielectric layer having a refractive index greater than or equal to 1.65.

Example 2: the optical structure of example 1 wherein the second transparent dielectric layer has a refractive index less than 1.65.

Example 3: the optical structure of any of examples 1-2, wherein the second transparent dielectric layer has a refractive index greater than or equal to 1.65.

Example 4: the optical structure of any one of examples 1-3, having a transmission peak comprising:

a maximum transmission of greater than 50%; and

a spectral bandwidth defined by a full width of the transmission peak at 50% of the maximum transmission,

wherein the maximum transmittance is at least 50%, and

wherein the spectral bandwidth of the transmission peak is greater than 2 nm.

Example 5: the optical structure of example 4, wherein the spectral bandwidth of the transmission peak is greater than or equal to about 10nm and less than or equal to about 200 nm.

Example 6: the optical structure of any one of examples 4-5, wherein the maximum transmission is at a wavelength between about 400nm and about 700 nm.

Example 7: the optical structure of any one of examples 4-6, further comprising a reflection peak comprising:

a maximum reflectance; and

a spectral bandwidth defined by the full width of the reflection peak at 50% of the maximum reflectance,

wherein the maximum reflectance is at least 50%, and

wherein the spectral bandwidth of the reflection peak is greater than 2 nm.

Example 8: the optical structure of example 7, wherein the spectral bandwidth of the reflection peak is greater than or equal to about 10nm and less than or equal to about 200 nm.

Example 9: the optical structure of any one of examples 7-8, wherein the maximum reflectance is at a wavelength between about 400nm and about 700 nm.

Example 10: the optical structure of any one of examples 7-9, wherein the maximum transmittance is at a first wavelength, and wherein the maximum reflectance is at a second wavelength different from the first wavelength.

Example 11: the optical structure of any one of examples 1-10, configured to display a first color when viewed by a typical human eye along a direction normal to a surface of the optical structure in a reflective mode and a second color different from the first color when viewed by a typical human eye along a direction normal to a surface of the optical structure in a transmissive mode.

Example 12: the optical structure of example 11, wherein the first color shifts to a third color when viewed by the average human eye in a direction angled away from a normal to the surface of the optical structure in a reflective mode.

Example 13: the optical structure of any of examples 11-12, wherein the second color shifts to a fourth color when viewed by the average human eye in a direction angled away from the normal to the surface of the optical structure in a transmissive mode.

Example 14: the optical structure of any one of examples 1-13, wherein the first metal layer or the second metal layer has a thickness greater than or equal to about 5nm and less than or equal to about 35 nm.

Example 15: the optical structure of any one of examples 1-14, wherein the second transparent dielectric layer has a thickness greater than or equal to about 100nm and less than or equal to about 2 microns.

Example 16: the optical structure of any one of examples 1-15, wherein first transparent dielectric layer or the third transparent dielectric layer has a thickness greater than or equal to about 100nm and less than or equal to about 500 nm.

Example 17: the optical structure of any one of examples 1-16, further comprising an encapsulation layer comprising silicon dioxide.

Example 18: the optical structure of example 17 wherein the silica is bonded to a silane coupling agent.

Example 19: the optical structure of example 18, wherein the silane coupling agent is configured to bond to an ink medium or a coating medium.

Example 20: the optical structure of any one of examples 1-19, wherein the first metal layer or the second metal layer comprises at least one of aluminum, silver, gold, a silver alloy, or a gold alloy.

Example 21: the optical structure of any one of examples 1-20, wherein the second transparent dielectric layer comprises a material having a refractive index less than 1.65, greater than 1.65, or equal to 1.65.

Example 22: the optical structure of any one of examples 1-21, wherein the second layer of transparent dielectric comprises at least one of SiO2, MgF2, or a polymer.

Example 23: the optical structure of any one of examples 1-22, wherein the first or third transparent dielectric layer comprises at least one of zinc oxide (ZnO), zinc sulfide (ZnS), zirconium dioxide (ZrO2), titanium dioxide (TiO2), tantalum pentoxide (Ta2O5), cerium dioxide (CeO2), yttrium oxide (Y2O3), indium oxide (In2O3), tin oxide (SnO2), Indium Tin Oxide (ITO), tungsten trioxide (WO3), or a combination thereof.

Example 24: the optical structure of any one of examples 1-23, wherein the first metal layer or the second metal layer has a thickness greater than or equal to about 5nm or less than or equal to about 35 nm.

Example 25: the optical structure of any one of examples 1-24, wherein the second transparent dielectric layer has a thickness greater than or equal to about 100nm or less than or equal to about 700 nm.

Example 26: the optical structure of any one of examples 1-25, wherein the first or third transparent dielectric layer has a thickness greater than or equal to about 100nm or less than or equal to about 500 nm.

Example 27: the optical structure of any one of examples 1-26, configured as a pigment, a coating, or an ink.

Example 28: the optical structure of any one of examples 1-27, further comprising a base layer configured to support the first dielectric layer, wherein the optical structure is configured as a film.

Example 29: the optical structure of example 28, wherein the base layer is flexible.

Example 30: the optical structure of any one of examples 28-29, wherein the base layer comprises a polymer.

Example 31: the optical structure of any one of examples 28-30, wherein the film is surrounded by a protective barrier.

Example 32: the optical structure of example 31 wherein the protective barrier comprises a UV curable resin.

Example 33: the optical structure of any one of examples 1-32, further comprising an encapsulation layer, wherein the optical structure is configured as a pigment, a coating, or an ink.

Example 34: the optical structure of example 33, wherein the encapsulation layer comprises silicon dioxide (SiO 2).

Example 35: the optical structure of any one of examples 33-34, further comprising a plurality of silica spheres embedded in the encapsulation layer.

Example 36: the optical structure of example 35, wherein the size of some of the plurality of silica spheres have a different size than other of the plurality of silica spheres.

Example 37: the optical structure of any one of examples 33-36, wherein the encapsulation layer is chemically attached to a silane coupling agent that includes a reactive group configured to chemically bond with an ink medium or a coating medium.

Example 38: the optical structure of example 37, wherein the ink medium or the coating medium comprises a material selected from the group consisting of: melamine acrylates, urethanes, polyesters, vinyl resins, acrylates, methacrylates, ABS resins, epoxy resins, styrene and alkyd based formulations and mixtures thereof.

Example 39: the optical structure of any one of examples 37-38, wherein the ink medium or the coating medium comprises a resin or a polymer.

Example 40: a banknote or document comprising an optical structure according to any one of examples 1 to 39.

Example 41: the banknote or document according to example 40, wherein the optical structure is configured to be attached to a ply of the banknote or document.

Example 42: the banknote or document according to example 40, wherein the optical structure is configured as a security thread inserted in the banknote or document.

Example 43: the banknote or document according to example 40, wherein the optical structure is configured as a tag attached to the banknote or document.

Example 44: the banknote or document of example 40, further comprising a window, wherein the optical structure is incorporated in the window.

Example 45: a document having a security feature, comprising:

a body of the document; and

an optical structure, comprising:

a second transparent dielectric layer disposed over the first metal layer;

a third transparent dielectric layer disposed over the second metal layer having a refractive index greater than or equal to 1.65,

wherein the optical structure is configured to display a first color in a reflective mode and a second color different from the first color in a transmissive mode.

Example 46: the security document of example 45, further comprising a second optical structure comprising:

a fourth transparent dielectric layer having a refractive index greater than or equal to 1.65;

a third metal layer disposed over the fourth transparent dielectric layer, the third metal layer having a third refractive index, wherein a ratio of a real part (n) of the third refractive index to an imaginary part (k) of the third refractive index (k) is greater than or equal to 0.01 and less than or equal to 0.5;

a fifth transparent dielectric layer disposed over the third metal layer;

a fourth metal layer disposed over the fifth transparent dielectric layer, the fourth metal layer having a fourth refractive index, wherein a ratio of a real part (n) of the fourth refractive index to an imaginary part (k) of the fourth refractive index is greater than or equal to 0.005 and less than or equal to 0.5; and

a sixth transparent dielectric layer having a refractive index greater than or equal to 1.65 disposed over the fourth metal layer,

wherein the second optical structure is configured to display a third color different from the first color and the second color in a reflective mode and a fourth color different from the first color, the second color, and the third color in a transmissive mode.

Example 47: the security document of example 46, wherein the optical structure or the second optical structure is configured as a film attached to the body of the document.

Example 48: the security document of any of examples 46-47, wherein the optical structure or the second optical structure is configured as a wire inserted into the body of the document.

Example 49: the security document of any of examples 46-48, wherein the optical structure or the second optical structure is configured as a ply disposed over the body of the document.

Example 50: the security document of any of examples 46-49, wherein the optical structure or the second optical structure is configured to contact an ink, dye, or paint of the body of the document.

Example 51: the security document of any one of examples 46-50, further comprising a first window including the optical structure and a second window including the second optical structure.

Example 52: the security document of any of examples 46-51, wherein the optical structure is configured as a two-color ink, two-color pigment, or two-color paint configured to produce a first color at a first viewing angle and a second color at a second viewing angle.

Example 53: the security document of any one of examples 46-52, wherein the document is printed with the bi-color ink, the bi-color pigment, or the bi-color paint.

Example 54: the security document of example 53, wherein the bi-color ink, the bi-color pigment, or the bi-color coating is disposed above, below, or mixed with a non-bi-color ink, pigment, or coating configured to produce the first color at the first and second viewing angles.

Example 55: the security document of example 54, wherein the non-bi-color, ink pigment, or paint forms a word, image, number, or symbol.

Example 56: the security document of example 55, wherein the text, the image, the number, or the symbol are not visible at the first viewing angle and are visible at the second viewing angle.

Example 57: a method of manufacturing a security feature configured to produce a first color in a reflective mode and a second color in a transmissive mode, the method comprising:

providing a base layer; and

disposing an optical structure on the base layer, the optical structure comprising:

a first transparent dielectric layer on the base layer, the first transparent dielectric layer having a refractive index greater than or equal to 1.65;

a second transparent dielectric layer disposed over the first metal layer;

a third transparent dielectric layer disposed over the second metal layer, the third dielectric layer having a refractive index greater than or equal to 1.65.

Example 58: the method of example 57, wherein disposing the optical structure on the base layer comprises:

coating the first transparent dielectric layer on the base layer;

depositing the first metal layer on the first transparent dielectric layer;

disposing the second transparent dielectric layer on the first metal layer;

depositing the second metal layer on the second transparent dielectric layer; and

disposing the third transparent dielectric layer on the second metal layer.

Example 59: the method of any one of examples 57-58, further comprising:

cutting the strip of the base layer having the optical structure; and

the strip was coated with a UV curable polymer to obtain a security thread.

Example 60: the method of any one of examples 57-58, further comprising:

removing the optical structure from the base layer;

fragmenting an optical structure into flakes having an area between five and about ten times the thickness of the optical structure;

encapsulating the sheet in an encapsulation layer comprising a plurality of silica spheres;

attaching a silane coupling agent to the encapsulation layer; and

mixing the flakes with an ink medium or a coating medium to obtain a two-color ink or a two-color coating.

Example 61: the method of any of examples 57-60, wherein the base layer is flexible.

Example 62: the method of any one of examples 57-61, wherein the base layer comprises a mesh.

Example 63: an optical structure, comprising:

a substrate;

a first optical structure over the substrate; and

a second optical structure over the substrate, the first and second optical structures at least partially overlapping,

wherein each of the first optical structure and the second optical structure comprises:

a second transparent dielectric layer disposed over the first metal layer;

a third transparent dielectric layer disposed over the second metal layer, the third transparent dielectric layer having a refractive index greater than or equal to 1.65,

wherein the thickness of the different layers of the first optical structure are configured to reflect a first color and transmit a second color different from the first color, and

wherein thicknesses of the different layers of the second optical structure are configured to reflect a third color different from the first color and transmit a fourth color different from the first color, the second color, or the third color.

Example 64: the optical structure of example 63, wherein the first optical structure completely overlaps the second optical structure.

Example 65: the optical structure of any one of examples 63-64, wherein the first and second optical structures are configured as films.

Example 66: the optical structure of any one of examples 63-65, wherein the first and second optical structures are configured as pigments.

Example 67: the optical structure of any one of examples 63-66, wherein the first and second optical structures are configured as plies.

Example 68: the optical structure of any one of examples 63-67, wherein the first and second optical structures are configured as a security thread.

Example 69: a document having a security feature, comprising:

a body of the document; and

a pigment disposed on the body, the pigment comprising:

an optical structure, comprising:

a first metal layer disposed over a first transparent dielectric layer, the first metal layer having a first refractive index, wherein a ratio of a real part (n) of the first refractive index to an imaginary part (k) of the first refractive index (k) is greater than or equal to 0.01 and less than or equal to 0.5;

a transparent dielectric layer disposed over the first metal layer; and

a second metal layer disposed over the transparent dielectric layer, the second metal layer having a second refractive index, wherein a ratio of a real part (n) of the second refractive index to an imaginary part (k) of the second refractive index is greater than or equal to 0.01 and less than or equal to 0.5; and

an encapsulation layer encapsulating the optical structure.

Example 70: the document of example 69, wherein the encapsulation layer comprises silicon dioxide.

Example 71: the document of any of examples 69-70, wherein the pigment produces a first color at a first viewing angle and a second color different from the first color at a second viewing angle.

Example 72: the document of any of examples 69-71, wherein the pigment comprises a resin configured to be chemically attached to the encapsulation layer.

Example 73: the document of any of examples 69-72, wherein the optical structure has a thickness, and wherein a length or width of the optical structure is at least 5 times the thickness.

Example 74: an optical structure, comprising:

a dielectric region having an outer surface enclosing a volume of dielectric material; and

a partially optically transmissive metal layer surrounding the outer surface of the dielectric region,

wherein a thickness of the optical structure has a value between about 100nm and about 2 microns,

wherein the optical structure has a lateral dimension between about 1 micron and about 20 microns, and

Example 75: the optical structure of example 74, further comprising a second dielectric region comprising one or more dielectric materials having a refractive index greater than about 1.65, the second dielectric region surrounding the partially optically transmissive metal layer.

Example 76: the optical structure of any one of examples 74-75, wherein the partially optically transmissive metal layer covers at least 80% of the outer surface of the dielectric region.

Example 77: the optical structure of any one of examples 74-76, wherein the partially optically transmissive metal layer covers at least 90% of the outer surface of the dielectric region.

Example 78: the optical structure of any one of examples 74-77, wherein the partially optically transmissive metal layer covers 100% of the outer surface of the dielectric region.

Example 79: the optical structure of any one of examples 74-78, wherein the dielectric region is spherical, elliptical, or circular.

Example 80: the optical structure of any one of examples 74-79, wherein the dielectric region is a cuboid or rectangular cuboid.

Example 81: the optical structure of any one of examples 74-80, wherein the dielectric region comprises particles.

Example 82: the optical structure of any one of examples 74-81, wherein the partially optically transmissive metal layer comprises silver.

Example 83: the optical structure of any one of examples 74-82, wherein the partially optically transmissive metal layer has a thickness between about 3nm and about 40 nm.

Example 84: the optical structure of any one of examples 74-83, wherein the dielectric region comprises silicon dioxide or titanium dioxide.

Example 85: the optical structure of any one of examples 75-84, wherein the second dielectric layer comprises a material having a refractive index greater than about 1.65.

Example 86: the optical structure of any one of examples 75-85, wherein the second dielectric layer comprises titanium dioxide.

Example 87: the optical structure of any one of examples 75-86, wherein the second dielectric layer covers at least 80% of the outer surface of the partially optically transmissive metal layer.

Example 88: the optical structure of any one of examples 75-87, wherein the second dielectric layer covers at least 90% of the outer surface of the partially optically transmissive metal layer.

Example 89: the optical structure of any one of examples 75-88, wherein the second dielectric layer covers at least 95% of the outer surface of the partially optically transmissive metal layer.

Example 90: the optical structure of any one of examples 75-89, wherein the second dielectric layer covers 100% of the outer surface of the partially optically transmissive metal layer.

Example 91: the optical structure of any one of examples 74-90, wherein the dielectric region comprises SiO₂。

Example 92: the optical structure of any one of examples 74-91, wherein the dielectric region comprises TiO₂。

Example 93: the optical structure of any one of examples 74-92, wherein the dielectric region comprises borosilicate having a high index of refraction metal oxide layer thereon.

Example 94: the optical structure of any one of examples 74-93, wherein the dielectric region comprises a layer having TiO thereon₂The borosilicate of (a).

Example 95: the optical structure of any one of examples 74-94, wherein the dielectric region comprises having SiO thereon₂The borosilicate of (a).

Example 96: the optical structure of any one of examples 74-95 included in a security thread or security ink.

Example 97: the optical structure of any one of examples 74-95 included in a film, a wire, a foil, or a ply.

Example 98: the optical structure of any one of examples 74-95 included in a flexible film having a flexible substrate.

Example 99: the optical structure of any one of examples 74-95 included in a pigment, a coating, or an ink.

Example 100: a security document comprising the optical structure of any of examples 74-99.

Example 101: a security document comprising the optical structure of any one of the examples 74-100, wherein the first color and the second color are complementary colors.

Example 102: a method of manufacturing a bi-color ink or bi-color coating configured to produce a first color in a reflective mode and a second color in a transmissive mode, the method comprising:

providing a base layer; and

a first metal layer disposed on the base layer, the first metal layer having a first refractive index, wherein a ratio of a real portion (n) of the first refractive index to an imaginary portion (k) of the first refractive index (k) is greater than or equal to 0/01 and less than or equal to 0.5;

a first transparent dielectric layer disposed over the first metal layer; and

a second metal layer disposed over the first transparent dielectric layer, the second metal layer having a second refractive index, wherein a ratio of a real part (n) of the second refractive index to an imaginary part (k) of the second refractive index is greater than or equal to 0.01 and less than or equal to 0.5.

Example 103: the method of example 102, further comprising:

removing the optical structure from the base layer;

fragmenting an optical structure into flakes having an area between five and about ten times the thickness of the optical structure; and

dispersing the flakes in an ink medium or a coating medium to obtain a two-color ink or a two-color coating.

Example 104: the method of example 103, further comprising encapsulating individual sheets in an encapsulation layer comprising a plurality of silicon dioxide balls.

Example 105: the method of example 104, further comprising attaching a silane coupling agent to the encapsulation layer.

Example 106: the method of any of examples 102-105, wherein the optical structure further comprises:

a second transparent dielectric layer between the base layer and the first metal layer, the second transparent dielectric layer having a refractive index greater than or equal to 1.65; and

Example 107: a bi-color ink or bi-color coating configured to produce a first color in a reflective mode and a second color in a transmissive mode, the bi-color ink or bi-color coating comprising:

a base layer; and

an optical structure on the base layer, the optical structure comprising:

a first metal layer disposed on the base layer, the first metal layer having a first refractive index, wherein a ratio of a real part (n) of the first refractive index to an imaginary part (k) of the first refractive index (k) is greater than or equal to 0.01 and less than or equal to 0.5;

a first transparent dielectric layer disposed over the first metal layer; and

Example 108: the bi-colored ink or bi-colored coating of claim 107, wherein the optical structure further comprises:

Example 109: the bi-colored ink or bi-colored coating of any one of claims 107-108, further comprising an ink medium or a coating medium comprising the optical structure, wherein the optical structure has a thickness of between 100nm and 2 microns, and wherein a lateral dimension of the optical structure is between 1 micron and 20 microns.

Example 110: an optical structure, comprising:

wherein the optical structure has a lateral dimension between about 100nm and about 20 microns, and

Example 111: the optical structure of example 110, further comprising a second dielectric region comprising one or more dielectric materials having a refractive index greater than about 1.65, the second dielectric region surrounding the partially optically transmissive metal layer.

Example 112: the optical structure of any one of examples 110-111, wherein the partially optically transmissive metal layer covers at least 80% of the outer surface of the dielectric region.

Example 113: the optical structure of any one of examples 110-112, wherein the partially optically transmissive metal layer covers at least 90% of the outer surface of the dielectric region.

Example 114: the optical structure of any one of examples 110-113, wherein the partially optically transmissive metal layer covers 100% of the outer surface of the dielectric region.

Example 115: the optical structure of any one of examples 110-114, wherein the dielectric region is spherical, elliptical, or circular.

Example 116: the optical structure of any one of examples 110-115, wherein the dielectric region is a cuboid or rectangular cuboid.

Example 117: the optical structure of any one of examples 110-116, wherein the dielectric region comprises particles.

Example 118: the optical structure of any one of examples 110-117, wherein the partially optically transmissive metal layer comprises silver.

Example 119: the optical structure of any one of examples 110-118, wherein the partially optically transmissive metal layer has a thickness between about 3nm and about 40 nm.

Example 120: the optical structure of any one of examples 110-119, wherein the dielectric region comprises silicon dioxide or titanium dioxide.

Example 121: the optical structure of any one of examples 111-120, wherein the second dielectric layer comprises a material having a refractive index greater than about 1.65.

Example 122: the optical structure of any one of examples 111-121, wherein the second dielectric layer comprises titanium dioxide.

Example 123: the optical structure of any one of examples 111-122, wherein the second dielectric layer covers at least 80% of the outer surface of the partially optically transmissive metal layer.

Example 124: the optical structure of any one of examples 111-123, wherein the second dielectric layer covers at least 90% of the outer surface of the partially optically transmissive metal layer.

Example 125: the optical structure of any one of examples 111-124, wherein the second dielectric layer covers at least 95% of the outer surface of the partially optically transmissive metal layer.

Example 126: the optical structure of any one of examples 111-125, wherein the second dielectric layer covers 100% of the outer surface of the partially optically transmissive metal layer.

Example 127: the optical structure of any one of examples 110-126, wherein the dielectric region comprises SiO₂。

Example 128: the optical structure of any one of examples 110-127, wherein the dielectric region comprises TiO₂。

Example 129: the optical structure of any one of examples 110-128, wherein the dielectric region comprises borosilicate having a high index of refraction metal oxide layer thereon.

Example 130: the optical structure of any one of examples 110-129, wherein the dielectric region comprises a layer having TiO thereon₂The borosilicate of (a).

Example 131: the optical structure of any one of examples 110-130, wherein the dielectric region comprises having SiO thereon₂The borosilicate of (a).

Example 132: the optical structure of any one of examples 110-131 included in a security thread or security ink.

Example 133: the optical structure of any one of examples 110-132 included in a film, a wire, a foil, or a ply.

Example 134: the optical structure of any one of examples 110-133 included in a flexible film having a flexible substrate.

Example 135: the optical structure of any one of examples 110-134 included in a pigment, coating, or ink.

Example 136: a security document comprising the optical structure of any of examples 110-135.

Example 137: a security document comprising the optical structure of any one of claims 110-136, wherein the first color and the second color are complementary colors.

Example 138: the optical structure of any one of examples 1-26, configured as a film, foil, wire, or ply.

Example 139: the optical structure of any one of examples 110-112, wherein the partially optically transmissive metal layer covers at least 95% of the outer surface of the dielectric region.

Example 140: the optical structure of any one of examples 74-76, wherein the partially optically transmissive metal layer covers at least 95% of the outer surface of the dielectric region.

Example 141: the security document of example 55, wherein the text, the image, the number, or the symbol are not visible at the second viewing angle and are visible at the first viewing angle.

Example 142: the method of example 58, wherein disposing the second transparent dielectric layer on the first metal layer comprises depositing the second transparent dielectric layer on the first metal layer.

Example 143: the method of example 58, wherein disposing the third transparent dielectric layer on the second metal layer comprises depositing the third transparent dielectric layer on the second metal layer.

Example 144: the method of example 57 or 58, further comprising:

removing the optical structure from the base layer;

attaching a silane coupling agent to the optical structure; and

Example 145: the method of example 144, further comprising:

encapsulating the sheet in an encapsulation layer; and

attaching the silane coupling agent to the encapsulation layer.

Example 146: the method of example 58, further comprising depositing the first metal layer on the first transparent dielectric layer using an electroless plating process.

Example 147: the method of example 58, further comprising depositing the second metal layer on the second transparent dielectric layer using an electroless plating process.

Example 148: a pigment, comprising:

an optical structure, comprising:

a transparent dielectric layer disposed over the first metal layer; and

a second metal layer disposed over the transparent dielectric layer, the second metal layer having a second refractive index, wherein a ratio of a real part (n) of the second refractive index to an imaginary part (k) of the second refractive index is greater than or equal to 0.01 and less than or equal to 0.5.

Example 149: the pigment of example 148, further comprising an encapsulation layer encapsulating the optical structure.

Example 150: the pigment of example 149, wherein said encapsulation layer comprises silicon dioxide.

Example 151: the pigment of any one of examples 148-150, further comprising a resin configured to be chemically attached to the encapsulation layer.

Example 152: the pigment of any one of examples 148-151, configured to produce a first color at a first viewing angle and a second color different from the first color at a second viewing angle.

Example 153: the pigment of any of examples 148-152, wherein the optical structure has a thickness, and wherein a length or width of the optical structure is at least 5 times the thickness.

Example 154: a document comprising the paint of any of examples 148-153, the document comprising a body and the paint disposed on the body.

Example 155: a package comprising the pigment of any of examples 148-153, the package comprising a body and the pigment disposed on the body.

Example 156: the optical structure of any one of examples 1-26, configured as a foil.

Example 157: the optical structure of any one of examples 1-26, configured as a wire.

Example 158: the optical structure of any one of examples 1-26, configured as a ply.

Example 159: the optical structure of any of examples 110-132 included in a line.

Example 160: the optical structure of any one of examples 110-132, included in a foil.

Example 161: the optical structure of any one of examples 110-132 included in a ply.

Drawings

Example embodiments will now be described in conjunction with the drawings.

FIG. 1 schematically illustrates a side view of an optical structure configured for use as a security feature.

FIGS. 2A-1 and 2A-2 schematically illustrate side views of optical structures configured for use as security features in the form of sheets encapsulated with an encapsulation layer comprising, for example, SiO₂Layers and silica spheres.

FIGS. 2B-1 and 2B-2 illustrate a plurality of flakes dispersed in a polymer that can comprise an ink medium or a coating medium.

Fig. 3 illustrates a silane coupling agent bonded to the exposed surface of the encapsulation layer of the sheet. The other side of the silane coupling agent may also be bonded to a medium (e.g., a polymer in which flakes are dispersed).

Fig. 4 is a schematic illustration of the resulting node showing the propagating light incident on the optical structure and the field strength at the metal layer.

Fig. 5A and 5B illustrate transmission and reflection spectra of examples of optical structures.

Fig. 6A-6D and 7A-7D are a-b plots showing the color paths or changes in reflection and transmission, respectively, for four different example optical structures.

Fig. 8A and 8B illustrate the transmission spectrum and the reflection spectrum, respectively, of an example of an optical structure.

Fig. 8C and 8D illustrate the transmission spectrum and the reflection spectrum, respectively, of an example of an optical structure.

Fig. 8E and 8F illustrate the transmission spectrum and the reflection spectrum, respectively, of an example of an optical structure.

Fig. 8G illustrates a b values in CIELa b color space for an example of an optical structure in transmission mode for different viewing angles between 0 and 40 degrees with respect to a normal to a surface of the example of the optical structure.

Fig. 8H illustrates a b values in CIELa b color space for an example of an optical structure in reflection mode for different viewing angles between 0 and 40 degrees relative to a normal to a surface of the example of the optical structure.

Fig. 9A schematically illustrates a cross-sectional view of an embodiment of an optical structure configured to be used as a security feature. FIG. 9B schematically illustrates a cross-sectional view of another embodiment of an optical structure configured to be used as a security feature.

FIG. 10 is a schematic illustration of a ply structure including an optical structure affixed to a banknote.

FIG. 11A shows a banknote having two windows, each window including a different optical structure. Fig. 11B shows a security device having two at least partially overlapping windows, each window comprising a different optical structure.

Fig. 12 and 13 illustrate examples of security devices that include optical structures disposed under or over text, symbols, or numbers. The text, symbols or numbers become visible when the viewing angle is changed.

Detailed Description

To reduce counterfeiting, currency, documents (e.g., banknotes), and other items (e.g., products and packaging) may have security features that can be checked by the public to verify authenticity. In many cases, it may be advantageous if the security features are readily visible under various light conditions and without special lighting conditions. It may also be desirable for the security feature to have a distinctive characteristic that can be readily identified by the public within a period of 1 to 10 seconds. Additionally, it is often advantageous if the security features are not easily reproducible by electronic or photographic equipment (e.g., printers, copiers, cameras, etc.).

One example of a security feature employed in banknotes is watermarks, which have a relatively high degree of awareness in the public. One example of a watermark may be an image comprising light and dark areas, which can be easily seen by lifting a banknote to see the watermark in light transmission. However, watermarks can be easily copied and are therefore not very secure. Other examples of security features may use ink and motion type features that are not readily visible under low light conditions (e.g., in dimly lit bars, restaurants, etc.), have poor image resolution, and/or have slow optical movement relative to banknote movement. Thus, some existing security features tend to have more complex structures with more complex color changing effects. However, this approach may be disadvantageous when complex security devices are applied to banknotes or currency, as these complex security devices can confuse the average person seeking to differentiate the security features.

It may be advantageous to have a security feature with high contrast against the background that can be easily identified by the public under various light conditions including low light. Thus, the various security features disclosed may appear to have one color in reflection and a different color in transmission. These security features may be incorporated into the banknote. The customer, merchant or bank teller can lift the note against the light to easily verify the authenticity of the note. Further, in some implementations, the security features may be configured to exhibit color shifts and/or movement of identifiable features as the viewing angle changes to enhance security. These and other features are described in further detail herein.

Accordingly, various security features contemplated herein may include at least partially reflective and at least partially transmissive optical stacks and/or structures. The security features contemplated herein may be configured as coatings, threads, plies, foils, films, pigments, and/or inks and incorporated with banknotes or other items. Aspects of the invention described in this application also include systems and methods of fabricating at least partially reflective and at least partially transmissive optical structures and/or stacks. In some embodiments, such optical structures may be fabricated on a support or base layer or sheet, such as a web (e.g., a roll-coated web). The processes described herein may also include removing the fabricated optical structures and/or stacks from a support or base layer (e.g., a roller or sheet). Aspects of the invention described in this application further include methods and systems for including in pigments and inks optical structures and/or stacks that are at least partially reflective and at least partially transmissive, with a desired amount of durability and mechanical strength for further use in or on or incorporation into banknotes and other security devices/documents.

Fig. 1 schematically illustrates an optical structure 10 including a stack of layers that may be used as a security feature. The optical structure 10 includes at least two

metal layers

13 and 15. The at least two

metal layers

13 and 15 may include a metal having a ratio of a real part (n) of the refractive index to an imaginary part (k) of the refractive index less than 1. For example, the at least two

metal layers

13 and 15 may comprise metals having n/k values as follows: between about 0.01 and about 0.6, between about 0.015 and about 0.6, between about 0.01 and about 0.5, between about 0.01 and about 0.2, between about 0.01 and about 0.1, or any value within a range or sub-range defined by such values. Thus, the at least two

metal layers

13 and 15 may comprise silver, silver alloys, gold, aluminum or copper and their respective alloys. Nickel (Ni) and palladium (Pd) may be used in some implementations. However, in some cases, the at least two

metal layers

13 and 15 do not include chromium, titanium and/or tungsten or any metal having an n/k ratio greater than 0.6. In some cases, metal layers 13 and 15 may have a thickness greater than or equal to about 3nm and less than or equal to about 35 nm. For example, the thickness of the metal layers 13 and 15 may be greater than or equal to about 10nm and less than or equal to about 30nm, greater than or equal to about 15nm and less than or equal to about 27nm, greater than or equal to about 20nm and less than or equal to about 25nm, or any value within the ranges or subranges defined by these values. The thickness of the metal layer 13 may be equal to the thickness of the metal layer 15. Alternatively, the thickness of the metal layer 13 may be greater or less than the thickness of the metal layer 15.

A transparent dielectric layer 14 is sandwiched between the at least two

metal layers

13 and 15. The dielectric layer 14 may have a refractive index greater than, less than, or equal to 1.65. Materials having a refractive index greater than or equal to 1.65 for purposes of this application may be considered high refractive index materials and materials having a refractive index less than 1.65 for purposes of this application may be considered low refractive index materials. The transparent dielectric layer 14 may comprise inorganic materials including (but not limited to): silicon dioxide (SiO)₂) Alumina (Al)₂O₃) Magnesium fluoride (MgF)₂) Cerium fluoride (CeF)₃) Lanthanum fluoride (LaF)₃) Zinc oxide (ZnO), zinc sulfide (ZnS), zirconium dioxide (ZrO)₂) Titanium dioxide (TiO)₂) Tantalum pentoxide (Ta)₂O₅) Cerium oxide (CeO)₂) Yttrium oxide (Y)₂O₃) Indium oxide (In)₂O₃) Tin oxide (SnO)₂) Indium Tin Oxide (ITO) and tungsten trioxide (WO)₃) Or a combination thereof. The transparent dielectric layer 14 may comprise a polymer including, but not limited to, parylene, acrylate, and/or methacrylate. Without loss of generality, the transparent dielectric layer 14 may comprise a material having a refractive index greater than, less than, or equal to 1.65 and an extinction coefficient between 0 and about 0.5 such that it has low light absorption in the visible spectral range.

The dielectric layer 14 may have a thickness greater than or equal to about 75nm and less than or equal to about 2 microns. For example, the dielectric layer 14 may have a thickness as follows: greater than or equal to about 150nm and less than or equal to about 650nm, greater than or equal to about 200nm and less than or equal to about 600nm, greater than or equal to about 250nm and less than or equal to about 550nm, greater than or equal to about 300nm and less than or equal to about 500nm, greater than or equal to about 350nm and less than or equal to about 450nm, greater than or equal to about 700nm and less than or equal to about 1 micron, greater than or equal to about 900nm and less than or equal to about 1.1 micron, greater than or equal to about 1 micron and less than or equal to about 1.2 microns, greater than or equal to about 1.2 microns and less than or equal to about 2.0 microns, or any value in the ranges/subranges defined by these values. Without being bound by any particular theory, in various embodiments, the thickness of the dielectric layer 14 may be about a quarter or an integer multiple of a quarter wavelength of light (e.g., visible light) incident thereon. In various implementations, the thickness of the dielectric layer 14 may be, for example, 1/4, 3/4, 5/4, 7/4, 9/4, 10/4, etc., of the wavelength of visible light incident on the dielectric layer 14.

The optical structure 10 further includes: a transparent dielectric layer 12 disposed on a side of the metal layer 13 opposite the dielectric layer 14; and a transparent dielectric layer 16 disposed on the opposite side of the metal layer 15 from the dielectric layer 14. In some cases, layers 12 and 16 may comprise materials having a refractive index greater than or equal to 1.65. For example, layers 12 and 16 may comprise ZrO₂、TiO₂ZnS, ITO (indium tin oxide), CeO₂Or Ta₂O₃. Dielectric layers 12 and 16 may have thicknesses as follows: greater than or equal to about 100nm and less than or equal to about 400nm, greater than or equal to about 150nm and less than or equal to about 350nm, greater than or equal to about 200nm and less than or equal to about 300nm, or any value within the ranges/subranges defined by these values. The thickness of dielectric layer 12 may be equal to the thickness of dielectric layer 16. Alternatively, the thickness of the dielectric layer 12 may be greater or less than the thickness of the dielectric layer 16. The optical structure 10 may have a thickness of less than or equal to about 2 microns.

Fabricating the optical structure 10 may include providing a layer of dielectric material 12 (or a layer of dielectric material 16) and depositing a layer of metal 13 (or a layer of metal 15) over the layer of dielectric material 12 (or the layer of dielectric material 16). Metal layer 13 (or metal layer 15) may be deposited on dielectric material layer 12 (or dielectric material layer 16) using an electroless plating method discussed in further detail below. The metal layer 13 (or the metal layer 15) may be deposited as a continuous film, pellets, metal clusters, or island structures. Another dielectric layer 14 may then be disposed over the metal layer 13 (or metal layer 15). An initial layer of dielectric material 12 (or a layer of dielectric material 16) may be disposed and/or formed over the support. The support is also referred to herein as a base layer. The support may comprise a carrier. The support may comprise a sheet, such as a mesh. The support may comprise a substrate. The substrate may be a continuous PET sheet or other polymeric mesh structure. The support member may comprise a nonwoven fabric. The nonwoven fabric may be a flat, porous sheet comprising fibers. In some embodiments, the nonwoven fabric may be configured as a sheet or web structure joined together by mechanically, thermally, or chemically entangling the fibers or filaments. In some embodiments, the nonwoven fabric may comprise a perforated film (e.g., plastic or fused plastic film). In some embodiments, the nonwoven fabric may comprise synthetic fibers, such as polypropylene or polyester or glass fibers.

The support may be coated with a release layer including a release agent. The release agent is soluble in a solvent or water. The release layer may be water-soluble polyvinyl alcohol or an acrylate soluble in a solvent. The release layer may comprise a coating deposited by evaporation prior to deposition/formation of the layer of the optical structure, such as, for example, salt (NaCl) or cryolite (Na)₃AlF₆)。

In some embodiments of the support configured as a nonwoven fabric, the nonwoven fabric may be coated with a release layer. Such embodiments may be dipped or immersed in a solvent or water that acts as a release agent to dissolve or remove the release layer. A release agent (e.g., solvent or water) is configured to penetrate from the side of the nonwoven fabric opposite the side on which the optical structure is disposed to facilitate release of the optical structure rather than having to penetrate the optical structure. The optical structure is recovered from the solvent or water after dissolving the release layer. In some manufacturing methods, the recycled optical structure may then be processed into a pigment.

In one method of manufacture, the optical structure 10 may be manufactured (e.g., deposited or formed) on a coated web, a coated base layer, a coated carrier, or a coated substrate. The coating on the web, base layer, substrate, or carrier may be configured as a release layer to facilitate easy removal of the optical structure 10.

The optical structure 10 may be configured as a film or foil by being disposed over a substrate or other support layer having a thickness, for example, greater than or equal to about 10 microns and less than or equal to about 25 microns. For example, the substrate or support layer (e.g., a polyester substrate or support layer) can have a thickness greater than or equal to 12 microns and less than or equal to 22.5 microns, greater than or equal to 15 microns and less than or equal to about 20 microns. The substrate or support layer may comprise a material such as, for example, polyester, polyethylene, polypropylene, or polycarbonate. The support or support layer is itself dissolvable. For example, the support or support layer may also comprise polyvinyl alcohol that is soluble in water, for example. Thus, instead of using a release layer on the insoluble support web, the support web itself may comprise a soluble material. Thus, the support or support layer may dissolve to leave the optical coating. The optical structure 10 configured as a film or foil may be encapsulated with a polymer, such as a UV cured polymer, for example.

The optical structure 10 may include additional layers. For example, a thin protective layer may be disposed between metal layer 13 and dielectric layer 12 and/or between metal layer 15 and dielectric layer 16. The protective layer may comprise a material, such as NiCrO, for example_x、Si₃N₄、CeSnO₄And ZnSnO₄. The protective layer may have a thickness of between about 3 to 5 nm. The protective layer may advantageously increase the durability of the metal layers 13 and 15.

The optical structure 10 may be removed from a substrate, web, carrier, or support layer, other than a film, on which the optical structure 10 is fabricated and separated into flakes having a size suitable for a pigment or printing ink. In some embodiments, flakes having a size suitable for a pigment or printing ink may have an area, length, and/or width of about 5 to 10 times the thickness of the flakes. Thus, the flakes have a thickness of about 1 micron, and/or may have a width and/or length between about 5 microns and about 50 microns. For example, the width and/or the length can be greater than or equal to about 5 microns and less than or equal to about 15 microns, greater than or equal to about 5 microns and less than or equal to about 10 microns, greater than or equal to about 5 microns and less than or equal to about 40 microns, greater than or equal to about 5 microns and less than or equal to about 20 microns, or any value in the ranges/subranges defined by these values. Flakes having a length and/or width that is less than about 5-10 times the thickness of the flakes (e.g., such as having a length and/or width equal to the thickness of the flakes) can be oriented along their edges in a printing ink or pigment. This can be disadvantageous because pigments or printing inks comprising flakes oriented along their edges may not exhibit a desired color in the reflective and transmissive modes. Dimensions outside of these ranges (e.g., thickness, length, and/or width) are also possible.

Fig. 2A-1 illustrates an example of a sheet 20. The optical structures 10 are fragmented, cut, diced, or otherwise separated to obtain individual (e.g., micron-sized) slices or flakes. In some embodiments, the resulting sheet may be surrounded by an encapsulation layer 21. Encapsulation layer 21 may comprise a moisture resistant material, such as, for example, silicon dioxide. Encapsulation layer 21 may also include silicon dioxide balls 22 and 23. The silica spheres 22 and 23 may be the same size or have different sizes. The encapsulation layer 21 may help protect the at least two

metal layers

13 and 15 from corrosion. Additionally or alternatively, the encapsulation layer 21 may reduce the occurrence of delamination of the at least two

metal layers

13 and 15 from other layers of the optical structure 10. The optical structure 10, surrounded by the encapsulation layer 21 and possibly including the silica spheres 22 and 23, may be configured as a sheet 20 suitable for pigment or printing ink. The silica spheres 22 and 23 of the encapsulation layer 21 may help prevent the sheets from adhering to each other. Without the ball, the sheets may adhere together as the two slides adhere together. The balls 22 and 23 also prevent the sheet 20 from sticking to the printing rollers in the printer. One method of surrounding the optical structure 10 with the encapsulation layer 21 may rely on sol-gel techniques using Tetraethylorthosilicate (TEOS). In one method of forming the encapsulation layer 21, an alcohol-based solution of TEOS may be added in small amounts (e.g., one or more drops at a time) to a dispersion of the flakes in alcohol or water. The catalyst (e.g., acid or sodium hydroxide solution) may be added in small amounts (e.g., one or more drops at a time) to a dispersion of the flakes in alcohol or water. A dispersion of the flakes in alcohol or water can be heated to a temperature of about 50 to 70 c while stirring to convert the TEOS to a silica coating. However, other processes may be employed.

In some embodiments, the plurality of flakes 20 may form a pigment. In some cases, such pigments can be color shifted (e.g., the color reflected and/or transmitted changes with viewing angle or angle of incidence of light). In some embodiments, a non-color shifting pigment or dye may be mixed with the pigment. In some embodiments, the flakes 20 may comprise other materials to form a pigment. While some of the pigments discussed herein may provide a color shift as a function of viewing angle or angle of incidence of light, pigments that do not exhibit a color shift or produce very little color shift as a function of viewing angle or angle of incidence of light are also contemplated.

In some embodiments, flakes 20 may be added to a medium, such as a polymer 25 (e.g., a polymeric resin), to form a two-color ink, pigment, or coating, as shown in fig. 2B-1. The flakes may be suspended in the medium (e.g., polymer) 25. The flakes can be randomly oriented in the medium (e.g., polymer) 25, as shown in fig. 2B-1. During the printing process, in some cases, individual flakes may be oriented parallel to the surface of an object (e.g., paper) to which a pigment, paint, or bi-color ink is applied due to, for example, printing action, gravity, and/or surface tension of the normal drying process of the pigment, the paint, or the bi-color ink, as shown in fig. 2B-2. The medium 25 may include materials including, but not limited to, melamine acrylates, urethanes, polyesters, vinyls, acrylates, methacrylates, ABS resins, epoxies, styrenes, and alkyd-based formulations, and mixtures thereof. In some implementations, the medium 25 (e.g., a polymer) can have a refractive index that closely matches the refractive index of the encapsulating silicon dioxide layer 21 and/or the silica spheres so that the encapsulating layer and/or the silica spheres do not adversely affect the optical properties of the pigment, coating, or bi-color ink in the medium.

In various embodiments, the sheet 20 need not be surrounded by an encapsulation layer. In such embodiments, one or more flakes 20 that are not encapsulated by the encapsulation layer may be added to or mixed with an ink or pigment medium (e.g., varnish, polymeric resin, etc.) to obtain a bi-colored ink or pigment as discussed herein. In various embodiments, a bi-color ink or pigment may include a plurality of flakes 20. The optical structures 10 configured as a plurality of lamellae 20 may have different distributions of shapes, sizes, thicknesses and/or aspect ratios. The optical structure 10 configured as a plurality of lamellae 20 may also have different optical properties. For example, optical structures 10 configured as a plurality of sheets 20 may also have different color properties.

In some implementations, an optical structure including

only metal layers

13 and 15 and transparent dielectric layer 14, without high index of refraction

dielectric layers

12 and 16, as depicted in fig. 2A-2, may be configured as a flake as discussed above and dispersed in medium 25 as shown in fig. 2B-2 to produce a two-color printing ink, coating, or pigment as discussed above. In some implementations, a sheet comprising an optical structure including

only metal layers

13 and 15 and transparent dielectric layer 14, without high index of refraction

dielectric layers

12 and 16, need not be encapsulated in an encapsulation layer as discussed above.

A silane coupling agent may be bonded to the encapsulation layer 21 to form a functionalized sheet 30, as shown in fig. 3. The bonding of the silane coupling agent to the encapsulation layer may occur through a hydrolysis reaction. The silane coupling agent may bind to the polymer (e.g., polymeric resin) of the printing ink or coating medium such that the heterogeneous mixture of pigment and polymer does not separate during the printing process and generally functions in much the same way that a homogeneous medium would function. The printing ink or coating medium may include materials including, but not limited to, melamine acrylates, urethanes, polyesters, vinyl resins, acrylates, methacrylates, ABS resins, epoxy resins, styrene, and alkyd-based formulations and mixtures thereof. The silane coupling agent used may be similar to that sold by glaster Company (moleston, PA USA). In some embodiments, the silane coupling agent may include hydrolyzable groups, such as, for example, alkoxy, acyloxy, halogen, or amines. After the hydrolysis reaction (e.g., hydrolysis), reactive silanol groups are formed that can condense with other silanol groups (e.g., with the silica spheres or silica encapsulation of the encapsulation layer 21) to form siloxane linkages. The other end of the silane coupling agent includes an R group 31. The R group 31 may include a variety of reactive compounds including, but not limited to, compounds having a double bond, an isocyanate, or an amino acid moiety. The double bonds can form bonds with ink polymers (e.g., ink polymers based on acrylate, methacrylate, or polyester-based resins) via reaction of free radical chemistry. For example, isocyanate functional silanes, alkanolamine functional silanes, and amino substituted silanes may form urethane linkages.

Without loss of generality, in various embodiments of optical structures 10 configured as sheets that do not include an encapsulation layer, a silane coupling agent may be bonded to a substrate that includes a dielectric material suitable for bonding with a silane coupling agent (e.g., TiO)₂) One or both of the high refractive index

dielectric layers

12 and 16.

Without loss of generality, the optical structure 10 may be considered an interferometric stack or cavity. Ambient light incident on the surface of optical structure 10 is partially reflected from the various layers of optical structure 10 (as shown by rays 47 and 48 in fig. 4) and partially transmitted through the various layers of optical structure 10 (as shown by ray 49 in fig. 4). FIG. 4 illustrates an embodiment of an optical structure 10 including high index of refraction

dielectric layers

12 and 16, metal layers 13 and 15, and dielectric layer 14 encapsulated in an encapsulation layer 21. Some wavelengths of ambient light reflected from the various layers may interfere constructively and some other wavelengths of ambient light reflected from the various layers may interfere destructively. Similarly, some wavelengths of light transmitted through various layers may constructively interfere and some other wavelengths of ambient light transmitted through various layers may destructively interfere. Thus, the optical structure 10 appears colored when viewed in both the transmissive mode and the reflective mode. In general. The color and intensity of light reflected and transmitted through the optical structure 10 by the optical structure 10 may depend on the thickness and materials of the various layers of the optical structure 10. By varying the materials and thicknesses of the various layers, the color and intensity of light reflected by and transmitted through the optical structure 10 can be varied. Without being bound by any particular scientific theory regarding the operation of the optical structure 10, in general, the materials and thicknesses of the various layers may be configured such that some or all of the ambient light reflected by the various layers interferes such that a node 45 in the field 42 appears at the two

metal layers

13 and 15. Without being bound by any particular scientific theory, it should be noted that, in some cases, the wavelengths substantially equal to the thickness of the spacer layer (e.g., wavelengths within about ± 10% of the thickness of the spacer layer) will interfere such that a node 45 in the field 42 appears at the two

metal layers

13 and 15. For other wavelengths, node 45 may not be present. Thus, in some implementations, the two

metal layers

13 and 15 may not be visible in the reflective mode. Furthermore, without being bound by a particular scientific theory, based on the thicknesses of the two

metal layers

13 and 15 and the transparent dielectric layer 14, a portion of the incident light may be transmitted through the optical structure 10 due to the phenomenon of "induced transmission" or "induced transmission". Reflection and transmission spectral characteristics are discussed below.

Fig. 5A shows spectral plots for both transmission (curve 501a) and reflection (curve 503a) for a first example of optical structure 10. The materials of the various layers of the first example of the optical structure 10 and the thicknesses of the various layers of the first example of the optical structure 10 are provided in table 1 below. As indicated in table 1, the first example of the optical structure 10 includes two metal layers comprising silver. The two silver layers correspond to the at least two

metal layers

13 and 15 of the optical structure 10 shown in fig. 1. Both silver layers have the same thickness of 25 nm. A dielectric layer having a thickness of 300nm is sandwiched between the two silver layers. The dielectric layer comprises SiO having a refractive index of 1.47011₂. Comprising SiO₂Corresponds to the transparent layer 14 having a low refractive index (i.e., a refractive index of less than 1.65). ZrO (ZrO)₂The layers disposed opposite to each of the two silver layers facing the SiO₂On the side opposite the side of the layer. Comprising ZrO₂Each of the two layers of (a) has a thickness of 150 nm. ZrO as shown in Table 1 below₂Having a refractive index of 2.27413. Comprising ZrO₂Corresponds to

transparent layers

12 and 16 having a high refractive index (i.e., a refractive index greater than or equal to 1.65). A first example of an optical structure 10 is encapsulated in SiO₂In the matrix, as indicated in table 1. SiO2₂The substrate is used to simulate a printing medium or ink having a similar refractive index.

The transmission and reflection of light viewed at an angle of 0 degrees relative to the normal to the first example of the optical structure 10 is shown in fig. 5A. Reflection spectrum 503a (indicated as curve #1 in fig. 5A) and transmission spectrum 501a (indicated as curve #0 in fig. 5A) in a spectral range between about 400nm and about 700nm including the visible spectral range were obtained using simulation software from http:// thinfilm.

Parameter(s)

Curve #0

Curve #1

Table 1: parameters for the first example of an optical structure having a reflection spectrum and a transmission spectrum as shown in fig. 5A.

As can be seen in fig. 5A, transmission curve 501a (curve #0) has a peak with a maximum that occurs at a wavelength of about 520nm and reflection curve 503a has two peaks with a first maximum that occurs at a wavelength of 420nm and a second maximum that occurs at a wavelength of about 650 nm. The maximum of the transmission peak and the reflection peak is greater than 0.5, indicating that the transmission peak and the reflection peak have high intensity. In addition, the transmission peak and the reflection peak have bandwidths as measured at 50% of the maximum of the peak greater than about 20 nm. The bandwidth, as measured at 50% of the maximum of the peak, is called full width at half maximum (FWHM). It is observed from fig. 5A that the FWHM of the transmission peak is about 75 nm.

Based on the locations of the transmission and reflection peaks and the bandwidths of the transmission and reflection peaks, the optical structure 10 may be perceived by the general human eye as having a first color in the reflection mode and a second color in the transmission mode. In some cases, the first color and the second color may be complementary colors. In some cases, the transmission peak and the reflection peak of the wavelength range including the visible spectral range may have high intensity and a FWHM of greater than 2nm (e.g., a FWHM of greater than or equal to about 10nm, a FWHM of greater than or equal to about 20nm, a FWHM of greater than or equal to about 30nm, a FWHM of greater than or equal to about 40nm, a FWHM of greater than or equal to about 50nm, a FWHM of greater than or equal to about 60nm, a FWHM of greater than or equal to about 70nm, a FWHM of greater than or equal to about 100nm, a FWHM of greater than or equal to about 200nm, a FWHM of less than or equal to about 300nm, a FWHM of less than or equal to about 250nm, or any value in the ranges/subranges defined by these values).

One or more reflection peaks may be considered to have high intensity if the reflectance or reflectance of the peak in the visible wavelength range is greater than or equal to about 50% and less than or equal to about 100%. For example, one or more reflection peaks may be considered to have high intensity if the amount or reflectivity or reflectance of light reflected in the visible wavelength range is greater than or equal to about 55% and less than or equal to about 99%, greater than or equal to about 60% and less than or equal to about 95%, greater than or equal to about 70% and less than or equal to about 90%, greater than or equal to about 75% and less than or equal to about 85%, or any value in the ranges/subranges defined by these values.

One or more transmission peaks may be considered to have high intensity if the transmittance or transmittance of the peak in the visible wavelength range is greater than or equal to about 50% and less than or equal to about 100%. For example, one or more transmission peaks may be considered to have high intensity if the amount of transmitted light or transmittance in the visible wavelength range is greater than or equal to about 55% and less than or equal to about 99%, greater than or equal to about 60% and less than or equal to about 95%, greater than or equal to about 70% and less than or equal to about 90%, greater than or equal to about 75% and less than or equal to about 85%, or any value in the ranges/subranges defined by these values.

A first example of an optical structure 10 having a design as depicted in table 1 and having a reflection spectrum and a transmission spectrum as shown in fig. 5A appears green in the transmission mode and magenta in the reflection mode to the average human eye. Without loss of generality, in various implementations, it may be advantageous that peaks in the reflection spectrum and the transmission spectrum are non-overlapping as shown in fig. 5A and 5B so that a reflection peak with the highest possible reflectance or reflectance may be obtained in a region of the visible spectrum range and a transmission peak with the highest possible transmittance or transmittance may be obtained in a non-overlapping region of the visible spectrum range. Thus, the reflective and transmissive colors may be different and possibly complementary to each other, such as red and green, yellow and violet, blue and orange, green and magenta, for example.

The shapes of the transmission and reflection peaks, the locations of the maxima of the transmission and reflection peaks, the FWHM of the transmission and reflection peaks, and the like can be varied by varying the materials and/or thicknesses of the various layers of the optical structure 10. This can be observed from fig. 5B, which depicts a reflection spectrum 503B and a transmission spectrum 501B for a second example of the optical structure 10, the second example of the optical structure 10 having the same material composition as the first example of the optical structure 10 but with various layers having different thicknesses. The parameters of a second example of the optical structure 10 are provided in table 2 below. As shown from Table 2, including SiO in the second example of the optical structure 10₂And the thickness of the dielectric layer having a refractive index of 1.47011 is 400nm instead of 300nm in the first example of the optical structure 10. Further, two ZrO disposed on either side of each of the two silver layers₂Is 225nm in the second example of the optical structure 10 instead of 150nm in the first example of the optical structure 10.

Parameter(s)

Curve #0

Curve #1

Table 2: parameters for the second example of an optical structure having a reflection spectrum and a transmission spectrum as shown in fig. 5B.

Since it comprises SiO₂And ZrO₂The thickness of the dielectric layer of (a) varies between the second instance of the optical structure and the first instance of the optical structure, so a typical human eye will perceive the second instance of the optical structure when viewed along a direction normal to the surface of the second instance of the optical structure to appear green in the reflective mode and magenta in the transmissive mode.

The colors of the first and second examples of the optical structure 10 as perceived by the general human eye in the reflective and transmissive modes may be offset from the magenta and green colors described above at different viewing angles relative to the normal of the surfaces of the first and second examples of the optical structure 10. For example, the first example of optical structure 10 may appear yellow-green in the reflective mode and blue in the transmissive mode when viewed at an angle of about 35 degrees relative to a normal to a surface of the first example of optical structure 10. As another example, the second example of the optical structure 10 may appear lavender in the reflective mode and yellowish in the transmissive mode when viewed at an angle of about 35 degrees relative to a normal to a surface of the second example of the optical structure 10. Without loss of generality, the reflection peak and transmission peak may exhibit a blue shift towards shorter wavelengths as the viewing angle relative to the normal to the surfaces of the first and second examples of optical structure 10 increases.

Table 3: CIELab values for transmission mode when the first example of the optical structure with the parameters as described in table 1 was viewed at different viewing angles in the presence of a D65 light source.

Table 4: CIELab values for the reflection mode when the first example of the optical structure with the parameters as described in table 1 was viewed at different viewing angles in the presence of a D65 light source.

Tables 3 and 4 above provide the CIELa b values for the transmissive mode and the reflective mode, respectively, when the first example of the optical structure with the parameters as described in table 1 was viewed at different viewing angles in the presence of a D65 light source. Tables 5 and 6 below provide the CIELa b values for the transmissive mode and the reflective mode, respectively, when viewing a second example of an optical structure having the parameters described in table 2 at different viewing angles in the presence of a D65 light source. CIELab colors closely represent colors perceived by the general human eye. The CIELab color space mathematically describes the various colors perceived by the general human eye in three dimensions L of lightness, a for the color components green-red, and b for the color components from blue-yellow. The a-axis extends longitudinally in the plane from green (denoted by-a) to red (denoted by + a). The b-axis extends in the plane from blue (denoted by-b) to yellow (denoted by + b) along a lateral direction perpendicular to the a-axis. The luminance is represented by the L-axis perpendicular to the a-b plane. The luminance increases from black represented by L-0 to white represented by L-100. CIELab values for different viewing angles using the D65 illuminant were calculated using the Essential mechanical film software.

Table 5: CIELab values for transmission mode when the second example of the optical structure with the parameters as described in table 2 was viewed at different viewing angles in the presence of a D65 light source.

Table 6: CIELab values for the reflection mode when the second example of the optical structure with the parameters as described in table 2 was viewed at different viewing angles in the presence of a D65 light source.

The optical performance of two additional examples of optical structures having the parameters provided in tables 7 and 8 were analyzed. An additional example of an optical structure is designed using Essential mechanical thin film software. The material compositions and thicknesses for the various layers of the third example of the optical structure are provided in table 7 and the material compositions and thicknesses for the various layers of the fourth example of the optical structure are provided in table 8.

Table 7: the material composition and thickness of the various layers of the third example of the optical structure 10.

Table 8: the material composition and thickness of the various layers of the fourth example of the optical structure 10.

The material compositions of the various layers of the third and fourth examples of the optical structure 10 are the same as the material compositions of the various layers of the first and second examples of the optical structure 10. For example, similar to the first and second examples of optical structure 10, the third and fourth examples of optical structure 10 include SiO sandwiched by two silver layers₂A layer and a layer disposed on the two silver layers and facing the SiO₂ZrO on the side opposite the side of the layer₂And (3) a layer. However, the thicknesses of the various layers are different for the first, second, third, and fourth examples of the optical structure 10.

First of the optical structure 10Three examples include two silver layers having a thickness of 25nm, each silver layer sandwiching a layer having a thickness of 174.44nm and comprising SiO₂The dielectric layer of (2). A third example of an optical structure 10 includes a facing SiO layer on a silver layer₂ZrO on the side opposite the side of the layer₂And (3) a layer. Each ZrO2₂The layer has a thickness of 246.88 nm. The total thickness of the third example of the optical structure 10 is 718.21 nm.

A fourth example of the optical structure 10 includes two silver layers having a thickness of 25nm, each silver layer sandwiching a layer having a thickness of 261.66nm and comprising SiO₂The dielectric layer of (2). A fourth example of an optical structure 10 includes a facing SiO layer on a silver layer₂ZrO on the side opposite the side of the layer₂And (3) a layer. Each ZrO2₂The layer has a thickness of 123.44 nm. The total thickness of the fourth example of the optical structure 10 is 558.55 nm.

Fig. 6A illustrates a b values in the CIELa b color space for the first example of the optical structure 10 in reflection mode at different viewing angles between 0 degrees and 45 degrees with respect to the normal of the surface of the first example of the optical structure 10 having the parameters as described in table 1. It is observed from fig. 6A that the first example of the optical structure 10 appears magenta to the general human eye in the reflective mode at a viewing angle of 0 degrees with respect to the normal to the surface of the first example of the optical structure 10. As the viewing angle increases, the color reflected by the first instance of the optical structure 10 shifts along the curve 601a in the direction of the arrow towards yellow.

Fig. 6B illustrates a B values in the CIELa B color space for the second example of the optical structure 10 at different viewing angles between 0 degrees and 45 degrees with respect to the normal of the surface of the second example of the optical structure 10 having the parameters as described in table 2 in the reflective mode. It is observed from fig. 6B that the second example of the optical structure 10 appears yellow-green to the general human eye in the reflective mode at a viewing angle of 0 degrees with respect to the normal to the surface of the second example of the optical structure 10. As the viewing angle increases, the color reflected by the second instance of the optical structure 10 shifts along the curve 601b in the direction of the arrow toward magenta.

Fig. 6C illustrates a b values in the CIELa b color space for the third example of the optical structure 10 in reflection mode at different viewing angles between 0 degrees and 45 degrees with respect to the normal of the surface of the third example of the optical structure 10 having the parameters as described in table 7. It is observed from fig. 6C that the third example of the optical structure 10 appears green to the general human eye in the reflective mode at a viewing angle of 0 degrees with respect to the normal to the surface of the third example of the optical structure 10. As the viewing angle increases, the color reflected by the third instance of the optical structure 10 shifts by 35 ° in the direction of the arrow towards blue along curve 601 c. As the viewing angle increases to 35, the transmitted color shifts from red to orange. It should be noted that the various reflection and transmission color curves are shifted counterclockwise in the various a x b plots of fig. 6A to 6D and fig. 7A to 7D.

Fig. 6D illustrates a b values in the CIELa b color space for the fourth example of the optical structure 10 in reflection mode at different viewing angles between 0 degrees and 45 degrees with respect to the normal of the surface of the fourth example of the optical structure 10 having the parameters as described in table 8. It is observed from fig. 6D that the fourth example of the optical structure 10 appears yellow to the average human eye in the reflective mode at a viewing angle of 0 degrees with respect to the normal to the surface of the fourth example of the optical structure 10. As the viewing angle increases, the color reflected by the fourth instance of optical structure 10 shifts along curve 601d in the direction of the arrow towards gray. In transmission, the color seen at zero degrees is blue shifted 35 ° to magenta. This sample is configured as a two-color film/pigment with minimal color shift as the viewing angle is changed.

Fig. 7A illustrates a b values in the CIELa b color space for the first example of the optical structure 10 in transmission mode at different viewing angles between 0 degrees and 45 degrees with respect to the normal of the surface of the first example of the optical structure 10 having the parameters as described in table 1. It is observed from fig. 7A that the first example of the optical structure 10 appears green to the general human eye in the transmissive mode at a viewing angle of 0 degrees with respect to the normal to the surface of the first example of the optical structure 10. As the viewing angle increases, the color transmitted through the first instance of the optical structure 10 shifts along the curve 701a in the direction of the arrow toward violet.

Fig. 7B illustrates a B values in the CIELa B color space for the second example of the optical structure 10 at different viewing angles between 0 degrees and 45 degrees with respect to the normal of the surface of the second example of the optical structure 10 having the parameters as described in table 2 in the transmissive mode. It is observed from fig. 7B that the second example of the optical structure 10 appears purple to the general human eye in the transmissive mode at a viewing angle of 0 degrees relative to a normal to the surface of the second example of the optical structure 10. As the viewing angle increases, the color reflected by the second instance of the optical structure 10 shifts along curve 701b in the direction of the arrow towards green.

Fig. 7C illustrates a b values in the CIELa b color space for the third example of the optical structure 10 at different viewing angles between 0 degrees and 45 degrees with respect to the normal of the surface of the third example of the optical structure 10 having the parameters as described in table 7 in the transmissive mode. It is observed from fig. 7C that the third example of the optical structure 10 appears red to the general human eye in the transmissive mode at a viewing angle of 0 degrees with respect to the normal to the surface of the third example of the optical structure 10. As the viewing angle increases, the color reflected by the third instance of the optical structure 10 shifts along curve 701c in the direction of the arrow towards orange.

Fig. 7D illustrates a b values in the CIELa b color space for the fourth example of the optical structure 10 at different viewing angles between 0 and 45 degrees with respect to the normal of the surface of the fourth example of the optical structure 10 having the parameters as described in table 8 in the transmissive mode. It is observed from fig. 7D that the fourth example of the optical structure 10 appears blue to the average human eye in the transmissive mode at a viewing angle of 0 degrees with respect to the normal to the surface of the fourth example of the optical structure 10. As the viewing angle increases, the color reflected by the fourth instance of the optical structure 10 shifts along the curve 701d in the direction of the arrow toward magenta.

Optical structure 10 is considered to be illuminated by D65 illumination to produce the curves of fig. 6A-6D and 7A-7D.

Fig. 8A and 8B illustrate the transmission and reflection spectra, respectively, for a third example of an optical structure 10 having parameters as described in table 7. As shown in fig. 8A and 8B, a third example of the optical structure 10 has a peak transmission at about 650nm, while the reflectance is substantially uniform in a spectral region between about 400nm and about 600nm and decreases at about 650 nm.

Fig. 8C and 8D illustrate the transmission and reflection spectra, respectively, for a fourth example of the optical structure 10 having parameters as described in table 8. As shown in fig. 8C and 8D, a fourth example of the optical structure 10 has a peak transmission between about 470nm and about 480nm, while the reflectance is substantially uniform in the spectral region between about 520nm and about 700nm and decreases at about 470 nm.

The optical performance of an additional fifth example of the optical structure 10 was analyzed. A fifth example of an optical structure 10 comprises a glass substrate, comprising CeO over said substrate₂A first metal layer comprising aluminum over the first dielectric layer, CeO over the first metal layer₂A second dielectric layer comprising aluminum over the second dielectric layer, and a second metal layer comprising CeO over the second metal layer₂And a third dielectric layer. The thicknesses of the various metal layers and dielectric layers may be configured to appear blue/violet in transmission at viewing angles between about 0 degrees and about 40 degrees relative to a normal to a surface of the fifth example of optical structure 10 and yellow/green in reflection at viewing angles between about 0 degrees and about 40 degrees relative to a normal to a surface of the fifth example of optical structure 10.

Fig. 8E and 8F illustrate the transmission spectrum and the reflection spectrum, respectively, for the fifth example of the optical structure 10 discussed above. Fig. 8G illustrates a b values in CIELa b color space for the fifth example of optical structure for different viewing angles between 0 and 40 degrees with respect to the normal of the surface of the fourth example of optical structure 10 in the transmissive mode. It is observed from fig. 8G that the fifth example of the optical structure 10 appears blue to the average human eye in the transmissive mode at a viewing angle of 0 degrees relative to the normal to the surface of the fifth example of the optical structure 10. As the viewing angle increases, the color reflected by the fifth example of the optical structure 10 shifts along the curve 751a in the direction of the arrow toward violet.

Fig. 8H illustrates a b values in CIELa b color space for the fifth example of optical structure for different viewing angles between 0 and 40 degrees relative to the normal of the surface of the fifth example of optical structure 10 in the reflective mode. It is observed from fig. 8H that the fifth example of the optical structure 10 appears yellow to the average human eye in the reflective mode at a viewing angle of 0 degrees with respect to the normal to the surface of the fifth example of the optical structure 10. As the viewing angle increases, the color reflected by the fifth example of the optical structure 10 shifts along the curve 751b in the direction of the arrow towards green.

Various embodiments of optical structures that may be used as security features may include a dielectric region comprising one or more dielectric materials surrounded by a partially optically transmissive or partially reflective metal layer (e.g., partially reflective and partially transmissive metal layers). For example, the optical structure can include a dielectric region having a first major surface and a second major surface (e.g., top and bottom) and an edge (or side) therebetween. In addition to being disposed on the first and second major surfaces (e.g., top and bottom), the partially reflective and partially transmissive metal layers may also be disposed on edges (or sides). In various implementations, the dielectric region comprising one or more dielectric materials is optically transmissive and may be optically transparent in some configurations. In certain implementations, the region including one or more dielectric materials is surrounded by a partially optically transmissive and partially reflective metal layer. In various embodiments, one or more dielectric materials may include polymers, glasses, oxides (e.g., SiO)₂、TiO₂) Or other dielectric material. In various implementations, a dielectric region can include a dielectric substrate coated with one or more dielectric materials (e.g., layers) having a refractive index equal to, less than, or greater than a refractive index of the dielectric substrate. In various embodiments, the dielectric region may include a first dielectric material (e.g., a first dielectric layer) having a first refractive index surrounded by a second dielectric material (e.g., a second dielectric layer) having a second refractive index. The second refractive index may be equal to, less than, or greater than the first refractive index.

Fig. 9A and 9B illustrate different embodiments of such optical structures. Fig. 9A schematically illustrates a cross-sectional view of an embodiment of an optical structure 70a comprising a dielectric region 30a surrounded by a partially reflective and partially transmissive metal layer 35 a. The optical structure 70a shown in fig. 9A has a rectilinear (e.g., rectangular) cross-section. Fig. 9B schematically illustrates a cross-sectional view of another embodiment of an optical structure 70B comprising a dielectric region 30B surrounded by a partially reflective and partially transmissive metal layer 35B. The optical structure 70B shown in fig. 9B has a circular cross-section.

Dielectric regions 30a and/or 30b may comprise one or more dielectric materials, such as, for example, a polymer, magnesium fluoride, silicon dioxide, aluminum oxide, titanium oxide, cerium oxide, any transparent oxide material, any transparent nitride material, any transparent sulfide material, glass, a combination of any of these materials, or any other inorganic or organic material. The refractive index of one or more dielectric materials in dielectric regions 30a and/or 30b may have a value between about 1.35 and about 2.5. For example, the refractive index of one or more dielectric materials in dielectric regions 30a and/or 30b may have a value as follows: between about 1.38 and 1.48, between about 1.48 and about 1.58, between about 1.58 and about 1.78, between about 1.75 and about 2.0, between about 2.0 and about 2.25, between about 2.25 and about 2.5, or any value in any range/subrange defined by these values. In some embodiments, values outside of these ranges are also possible. Dielectric regions 30a and/or 30b may comprise a dielectric substrate coated with one or more dielectric materials having a refractive index equal to, less than, or greater than the refractive index of the dielectric substrate. In various implementations, the dielectric regions 30a and/or 30b may comprise a first dielectric material having a first refractive index surrounded by a second dielectric material having a second refractive index. The second refractive index may be equal to, less than, or greater than the first refractive index.

In various implementations, the dielectric regions 30a and/or 30b can be configured as plates, sheets, spheres, ellipsoids, discs, or any other 3-dimensional shape that encloses a volume. The dielectric regions 30a and/or 30b may have regular or irregular shapes. For example, as shown in fig. 9A, the dielectric region 30a may be configured as a flat plate having two

major surfaces

31a and 31b and one or more edge surfaces disposed between the two

major surfaces

31a and 31 b. In some implementations, a number of edge surfaces can be disposed between the two

major surfaces

31a and 31 b. The number of edge surfaces may be, for example, one, two, three, four, five, six, seven, eight, nine, ten, twelve, twenty, thirty, fifty, etc., or in any range between any of these values. Values outside of these ranges are also possible. The

main surfaces

31a and 31b may have various shapes. For example, in certain implementations, one or both of

major surfaces

31a and 31b can have a linear or curvilinear shape. In certain embodiments, the shape may be regular or irregular. For example, one or both of

major surfaces

31a and 31b may have a square shape, a rectangular shape, a circular shape, an oval shape, an elliptical shape, a pentagonal shape, a hexagonal shape, an octagonal shape, or any polygonal shape. In various implementations, one or both of

major surfaces

31a and 31b can have serrated edges such that the lateral dimension (e.g., length or width) of one or both of

major surfaces

31a and 31b varies across an area of one or both of

major surfaces

31a and 31 b. Other configurations are also possible. In addition, other shapes are possible. One or more of the edge surfaces may have various shapes (e.g., viewed from the side), such as a square shape, a rectangular shape, an oval shape, an elliptical shape, a pentagonal shape, a hexagonal shape, an octagonal shape, or any polygonal shape.

In certain implementations, the shape of one or more of the edge surfaces (e.g., viewed from the side) can be straight or curved. In certain embodiments, the shape may be regular or irregular. Similarly, the cross-section of dielectric regions 30a and/or 30b parallel to one of

major surfaces

31a and 31b may be straight or curved in certain implementations and may be regular or irregular in certain implementations. For example, the cross-section may have a square shape, a rectangular shape, a circular shape, an oval shape, an elliptical shape, a pentagonal shape, a hexagonal shape, an octagonal shape, or any polygonal shape. Other shapes are also possible. Likewise, the cross-section of the dielectric material or regions 30a and/or 30b perpendicular to one of the

surfaces

31a and 31b may be straight or curved in certain implementations and may be regular or irregular in certain implementations. For example, the cross-section may have a square shape, a rectangular shape, a circular shape, an oval shape, an elliptical shape, a pentagonal shape, a hexagonal shape, an octagonal shape, or any polygonal shape. Other shapes are also possible. In various implementations, the area, length, and/or width of

major surfaces

31a and 31b of dielectric region 30a may be greater than or equal to about 2, 3, 4, 5, 6, 8, or 10 times the thickness of dielectric region 30a and less than or equal to about 50 times the thickness of dielectric region 30a, or any value in a range/subrange between any of these values. Accordingly, the dielectric region 30a may have a large aspect ratio.

In some implementations, the thickness (T) of the dielectric region 30a can correspond to the distance between the two

major surfaces

31a and 31b along the vertical direction, as shown in fig. 9A. As another example, as shown in fig. 9B, the dielectric material 30B may be configured as a sphere. The thickness of the dielectric material 30b configured as a sphere may correspond to the diameter of the sphere. In other implementations, the dielectric materials 30a and/or 30b may be configured as cubes, rectangular cuboids, cylinders, ellipsoids, ovoids, or any other three-dimensional shape. In certain embodiments, the shape may be curvilinear or rectilinear. In certain embodiments, the shape may be regular or irregular. Thus, in some implementations, the dielectric regions 30a and/or 30b may be configured as irregularly shaped objects that enclose a volume of one or more dielectric materials.

In various implementations, light can be transmitted through the

optical structures

70a and 70b and reflected by the surface of the

optical structure

70a or 70 b. Further, in various implementations, the dielectric regions 30a and/or 30b can have a thickness that allows light incident on one side of the metal layers 35a and/or 35b to constructively or destructively interfere. For example, in various implementations, the thickness of the dielectric regions 30a and/or 30b can be approximately one-quarter of a wavelength or an integer multiple of a quarter wavelength of light (e.g., visible light) incident thereon. In various implementations, the thickness of the dielectric regions 30a and/or 30b may be, for example, 1/4, 3/4, 5/4, 7/4, 9/4, 10/4, etc., of the wavelength of visible light incident on the

dielectric material

30a or 30 b. Thus, incident light of various wavelengths may constructively or destructively interfere when transmitted through

optical structure

70a or 70b or reflected by

optical structure

70a or 70 b. Thus, in some configurations, when white light is incident on the optical structure, colored light is reflected and/or transmitted through the optical structure by the optical structure. In some implementations, when white light is incident on the optical structure, a first color is reflected and a second, different color is transmitted. In some cases, the first color and the second color may be complementary.

In various implementations, the thickness (or lateral dimension) of dielectric regions 30a and/or 30b can have a value between about 90nm and about 2 microns, for example, to obtain constructive interference of incident visible light. In various implementations, the thickness (or lateral dimension) of the dielectric regions 30a and/or 30b may be greater than or equal to about 90nm and less than or equal to about 1 micron, greater than or equal to about 100nm and less than or equal to about 1.0 micron, greater than or equal to about 300nm and less than or equal to about 1.0 micron, greater than or equal to about 400nm and less than or equal to about 900nm, greater than or equal to about 500nm and less than or equal to about 800nm, greater than or equal to about 600nm and less than or equal to about 700nm, or any thickness in any range/subrange defined by these values. In some embodiments, values outside of these ranges are also possible.

Dielectric materials 30a and/or 30b may be purchased from different suppliers, such as tyndall institute, glass flakes Ltd, Sigma technology (Sigma Technologies), or customized by synthesis in a laboratory or manufacturing facility. In some implementations, the optical structure 70a (or 70b) and/or the dielectric region 30a (or 30b) can include flakes (e.g., as can be obtained from glass flakes, Inc. http:// www.glaCom/p agents/home glass flakes). In some embodiments, the flakes can comprise glass, for example, such as may or may not be coated (e.g., high refractive index metal oxides, such as TiO)₂And/or silica) with an average thickness between about 90nm and about 2 microns (e.g., an average thickness of about 1.2 microns). In various embodiments, the lateral dimensions (e.g., length and width) of the scale can be between about 5 microns and about 20 microns. In some embodiments, values outside of these ranges are also possible.

As discussed above, the

dielectric region

30a or 30b may be surrounded by a partially reflective and partially transmissive

metal layer

35a or 35 b. In some embodiments, the

metal layer

35a or 35b may comprise a metal having a ratio of the real part of the refractive index (n) to the imaginary part of the refractive index (k) that is less than 1 as discussed above. For example,

metal layer

35a or 35b may comprise a metal having an n/k value as follows: between about 0.01 and about 0.6, between about 0.015 and about 0.6, between about 0.01 and about 0.5, between about 0.01 and about 0.2, between about 0.01 and about 0.1, or any value within a range or sub-range defined by such values. In some embodiments, values outside of these ranges are also possible. Accordingly, the

metal layer

35a or 35b may include silver, silver alloy, gold, aluminum or copper and their respective alloys, nickel (Ni) and palladium (Pd).

In various implementations, the thickness of the

metal layer

35a or 35b can be configured such that the

metal layer

35a or 35b is at least partially transmissive and partially reflective to light in the visible spectral region between about 400nm and about 800 nm. For example, the thickness of the metal layer 35 may be configured such that the

metal layer

35a or 35b is at least partially transmissive to light in the following wavelength ranges: between about 400nm and about 500nm, between about 430nm and about 520nm, between about 450nm and about 530nm, between about 520nm and about 550nm, between about 540nm and about 580nm, between about 550nm and about 600nm, between about 600nm and about 680nm, between about 630nm and about 750nm, or any wavelength in a range/subrange defined by any of these values. In some embodiments, values outside of these ranges are also possible. Alternatively or additionally, the thickness of the

metal layer

35a or 35b may be configured such that the

metal layer

35a or 35b is at least partially reflective to light in the following wavelength ranges: between about 400nm and about 500nm, between about 430nm and about 520nm, between about 450nm and about 530nm, between about 520nm and about 550nm, between about 540nm and about 580nm, between about 550nm and about 600nm, between about 600nm and about 680nm, between about 630nm and about 750nm, or any wavelength in a range/subrange defined by any of these values. In some embodiments, values outside of these ranges are also possible.

The thickness of the

metal layer

35a or 35b may vary depending on the type of metal. For example, in embodiments of the

optical structure

70a or 70b that include the metal (e.g., silver)

layer

35a or 35b, the thickness of the metal (e.g., silver)

layer

35a or 35b can be greater than or equal to about 10nm and less than or equal to about 35nm such that the metal (e.g., silver)

layer

35a or 35b can be partially transmissive to light in the visible spectral range. In some implementations, the thickness of the

metal layer

35a or 35b may be less than about 10nm or greater than about 35nm, which may depend on the type of metal used and the wavelength range in which transmittance or transmittance is desired. Thus, in various embodiments, the

metal layer

35a or 35b may have a thickness greater than or equal to about 3nm and less than or equal to about 40 nm. In some embodiments, values outside of these ranges are also possible. As discussed above, with reference to fig. 4, the thicknesses of the

metal layer

35a or 35b and the

dielectric region

30a or 30b may be configured such that interference of some or all of the incident light reflected by one or more layers of the

metal layer

35a or 35b and the

dielectric region

30a or 30b may create a node at or in the

metal layer

35a or 35 b. Accordingly, the transmittance through the

metal layer

35a or 35b may be greater than expected for a particular thickness of the

metal layer

35a or 35 b. Without being bound by any particular scientific theory, this effect is referred to as induced transmittance. Due to induced transmittance or induced transmission, in some implementations, the

optical structure

70a or 70b can be configured to exhibit a first color in the reflective mode and a second color in the transmissive mode.

Depending on the shape of the

dielectric region

30a or 30b, the

dielectric region

30a or 30b may have one or more outer surfaces. The

metal layer

35a or 35b may cover or substantially cover all or a small portion of the outer surface of the

dielectric region

30a or 30 b. Thus, in various implementations, the

metal layer

35a or 35b may be disposed over at least 50% of one or more outer surfaces of the

dielectric region

30a or 30 b. For example, the

metal layer

35a or 35b may be disposed over at least 50%, at least 60%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 99%, 100%, or any range between any of these values of one or more outer surfaces of the

dielectric region

30a or 30 b. In some implementations, the

metal layer

35a or 35b can be disposed over an entire area (e.g., 100%) of one or more outer surfaces of the

dielectric region

30a or 30 b. Without being bound by any particular theory, the optical properties of the

optical structure

70a or 70b may vary based on the amount of the outer surface of the

dielectric region

30a or 30b covered by the

metal layer

35a or 35 b. For example, the reflectivity or reflectance and/or transmittance of the

optical structure

70a or 70b may vary based on the amount of the outer surface of the

dielectric region

30a or 30b covered by the

metal layer

35a or 35 b.

In various implementations, the shape of the

metal layer

35a or 35b can conform to the shape of the underlying

dielectric material

30a or 30 b. For example, in the optical structure 70a shown in fig. 9A, the dielectric material 30a has a rectangular cross-section. Thus, the metal layer 35a disposed over the

major surfaces

31a and 31b and the edge surfaces also has a rectangular cross section. As another example, in the optical structure 70B shown in fig. 9B, the dielectric material 30B has a circular cross-section. Thus, the metal layer 35b disposed over the circumference of the dielectric material 30b also has a circular cross-section. However, in other implementations, the shape of the

metal layer

35a or 35b may be different from the shape of the underlying

dielectric material

30a or 30 b.

In various embodiments, the

optical structure

70a or 70b comprising the

dielectric region

30a or 30b surrounded by the

metal layer

35a or 35b may be configured as a particle, a plate, a filament, a flake, a bead (e.g., a spherical bead), or a flake as discussed above. In some embodiments, the

optical structure

70a or 70b including the

dielectric region

30a or 30b surrounded by the

metal layer

35a or 35b may have the same shape as that of the

dielectric region

30a or 30 b. For example, as shown in fig. 9A, when the dielectric region 30a is configured as a cuboid or rectangular cuboid, the optical structure 70a may be configured as a cuboid or rectangular cuboid. As another example, when the dielectric region 30B is configured as a sphere, the optical structure 70B may be configured as a sphere, as shown in fig. 9B. In some cases,

optical structures

70a or 70b configured as particles, plates, flakes, filaments, or flakes may be suitable for use in pigments or printing inks. In some embodiments, the

optical structures

70a or 70b configured as particles, plates, scales, filaments, or flakes may have an area (or lateral dimension) of about 5 to 10 times or more the thickness of the

optical structures

70a or 70b configured as particles, plates, scales, filaments, or flakes. Thus, an

optical structure

70a or 70b configured as a particle, slab, flake, filament, or sheet may have a thickness between about 100nm and about 1 micron. In some such embodiments, the area (or lateral dimension) may be greater than or equal to about 500nm and less than or equal to about 1 micron, greater than or equal to about 1 micron and less than or equal to about 5 microns, greater than or equal to about 5 microns and less than or equal to about 10 microns, greater than or equal to about 5 microns and less than or equal to about 40 microns, greater than or equal to about 5 microns and less than or equal to about 20 microns, or any value in the ranges/subranges defined by these values. In various embodiments, the

optical structures

70a or 70b configured as particles, slabs, scales, filaments, or flakes may be configured such that the area, length, and/or width of the major surface of the

optical structure

70a or 70b is greater than or equal to about 2, 3, 4, 5, 6, 8, or 10 times the thickness of the

optical structure

70a or 70b and less than or equal to about 50 times the thickness of the

optical structure

70a or 70b or any value in any range formed by any of these values.

In various implementations, surrounding the

dielectric region

30a or 30b with the

metal layer

35a or 35b may advantageously increase the reflectivity or reflectance of the

dielectric material

30a or 30b at one or more wavelengths in the visible spectral range in some implementations. In some implementations, surrounding the

dielectric material

30a or 30b with the

metal layer

35a or 35b can advantageously enhance or change the color appearance of the

dielectric material

30a or 30b in the reflective mode and the transmissive mode at one or more wavelengths of the visible spectral range.

In various implementations, an

optical structure

70a or 70b including a

dielectric region

30a or 30b surrounded by a

metal layer

35a or 35b can have a reflection spectrum having one or more reflection peaks in the visible region of the spectrum and a transmission spectrum having one or more transmission peaks in the visible region of the spectrum. Without loss of generality, the one or more reflection peaks and the one or more transmission peaks do not overlap each other. Thus, an

optical structure

70a or 70b comprising a

dielectric region

30a or 30b surrounded by a

metal layer

35a or 35b may have a first color in the reflective mode and a second color different from the first color in the transmissive mode. In certain implementations, the first and second hues can be complementary colors, such as, for example, red and green, yellow and violet, blue and orange, green and magenta, and the like.

In various implementations, there may be little to no shift in the first color in the reflective mode for any viewing angle between a first angle relative to a normal to the surface of the

optical structure

70a or 70b and a second angle relative to a normal to the surface of the

optical structure

70a or 70 b. Likewise, in some embodiments, there may be little to no shift in the second color in the transmissive mode for any viewing angle between a first angle relative to the normal to the surface of

optical structure

70a or 70b and a second angle relative to the normal to the surface of

optical structure

70a or 70 b. In various embodiments, the first angle may have a value between 0 degrees and 10 degrees (e.g., 0 degrees, 1 degree, 2 degrees, 3 degrees, 4 degrees, 5 degrees, 6 degrees, 7 degrees, 8 degrees, 9 degrees, or 10 degrees). In various embodiments, the second angle may have a value between 20 degrees and 90 degrees (e.g., 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees, or 90 degrees). Thus, for any viewing angle between a first angle (e.g., 0, 1, 2, 3, 4, 5, 6, 7,8, 9, or 10 degrees) relative to the normal to the surface of the

optical structure

70a or 70b and a second angle (e.g., 20, 30, 40, 50, 60, 70, 80, or 90 degrees) relative to the normal to the surface of the

optical structure

70a or 70b, the color of the

optical structure

70a or 70b may remain substantially the same in the reflective mode and/or the transmissive mode. Likewise, in some implementations, there may be little to no offset color shift in the color of the

optical structures

70a or 70b in the reflective mode and/or the transmissive mode for tilt angles of 10 degrees, 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees, or 90 degrees, or any value in a range/sub-range defined by any of these values.

In some implementations, it may be desirable to have a color shift of a first color in the reflective mode when the viewing angle changes from a first angle relative to the normal of the surface of the

optical structure

70a or 70b to a second angle relative to the normal of the surface of the

optical structure

70a or 70 b. Similarly, in various embodiments, a color shift of a second color in the transmissive mode may be desired when the viewing angle changes from a first angle relative to the normal to the surface of the

optical structure

70a or 70b to a second angle relative to the normal to the surface of the

optical structure

70a or 70 b. In various embodiments, the first angle may have a value between 0 degrees and 10 degrees (e.g., 0 degrees, 1 degree, 2 degrees, 3 degrees, 4 degrees, 5 degrees, 6 degrees, 7 degrees, 8 degrees, 9 degrees, or 10 degrees). In various embodiments, the second angle may have a value between 20 degrees and 90 degrees (e.g., 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees, or 90 degrees), depending on the design. Thus, the color of the

optical structure

70a or 70b may change (e.g., dark blue to light blue, purple to pink, dark green to light green, etc.) in the reflective mode and/or the transmissive mode when the viewing angle changes from a first angle (e.g., 0 degrees, 1 degree, 2 degrees, 3 degrees, 4 degrees, 5 degrees, 6 degrees, 7 degrees, 8 degrees, 9 degrees, or 10 degrees) relative to the normal of the surface of the

optical structure

70a or 70b to a second angle (e.g., 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees, or 90 degrees) relative to the normal of the surface of the

optical structure

70a or 70 b. Likewise, in some implementations, there may be a shift in the color of the

optical structure

Without being bound by any particular theory, one or more reflection peaks of the reflection spectrum of the

optical structure

70a or 70b including the

dielectric region

30a or 30b surrounded by the

metal layer

35a or 35b may have a high reflectivity or reflectance. For example, the reflectance or reflectance of the one or more reflection peaks may be greater than or equal to 30%, greater than or equal to 40%, greater than or equal to 50%, greater than or equal to 55%, greater than or equal to 60%, greater than or equal to 65%, greater than or equal to 70%, greater than or equal to 75%, greater than or equal to 80%, greater than or equal to 85%, greater than or equal to 90%, greater than or equal to 95%, and less than or equal to 100%, or a value in any range/subrange defined by these values.

Without being bound by any particular theory, one or more transmission peaks of the transmission spectrum of the

optical structure

70a or 70b including the

dielectric region

30a or 30b surrounded by the

metal layer

35a or 35b may have a high transmission or transmittance. For example, the transmittance or transmittance of the one or more transmission peaks may be greater than or equal to 30%, greater than or equal to 40%, greater than or equal to 50%, greater than or equal to 55%, greater than or equal to 60%, greater than or equal to 65%, greater than or equal to 70%, greater than or equal to 75%, greater than or equal to 80%, greater than or equal to 85%, greater than or equal to 90%, greater than or equal to 95%, and less than or equal to 100%, or a value in any range/subrange defined by these values.

Optical structure

70a or 70b, including

dielectric region

30a or 30b surrounded by

metal layer

35a or 35b, may produce many or all of the optical effects described above with reference to optical structure 10 (e.g., as shown in fig. 1) in which both

metal layers

13 and 15 do not surround dielectric layer 14.

The

metal layer

35a or 35b may be disposed around the

dielectric material

30a or 30b using various chemical methods. For example, the metal layer 35a or 36b may be disposed around the

dielectric region

30a or 30b using an electroless plating method. Respective embodiment of electroless plating method for depositing metal layer 35a or 36bEmbodiments may include depositing the

metal layer

35a or 35b without applying a current or voltage. Various metals such as, for example, gold, silver, or nickel, may be deposited using electroless plating methods. An example of depositing a

metal layer

35a or 35b comprising silver around the

dielectric region

30a or 30b using an electroless plating method is discussed below. Electroless plating methods of depositing silver may also be referred to as electroless silver plating. Electroless silver plating includes immersing the

dielectric region

30a or 30b in a silver plating bath including a chemical compound of silver (e.g., silver nitrate, silver ammonia compound, sodium silver cyanide, etc.) and at least one of ammonia, water, potassium hydroxide, or sodium hydroxide. Reducing a chemical compound of silver to metallic silver using a reducing agent added to the silver plating bath. The metallic silver adheres to the exposed surface of the

dielectric region

30a or 30 b. The reducing agent may include glucose, sucrose, invert sugar, stannous chloride, hydrazine, Rochelle salts, formaldehyde, or an organoborane (e.g., dimethylamine borane in various embodiments). In certain embodiments, a silver plating bath and reducing agent may be sprayed on the

dielectric regions

30a or 30 b. In some embodiments, tin dichloride (SnCl) may be used₂) The outer surface of the

dielectric region

30a or 30b is activated in preparation for electroless deposition of the metal layer. Other methods of depositing the

metal layer

35a or 35b on the outer surface of the

dielectric region

30a or 30b may also be used. For example, the

metal layer

35a or 35b may be disposed around the

dielectric region

30a or 30b using methods such as Chemical Vapor Deposition (CVD), sputtering, or electroplating, for example. In some implementations, the

metal layer

35a or 35b can be patterned around the

dielectric region

30a or 30 b.

In various implementations, a second

dielectric region

40a or 40b comprising one or more dielectric materials can be disposed around the metal-coated

dielectric region

30a or 30 b. The second

dielectric region

40a or 40b may comprise a high refractive index material, such as ZrO₂、TiO₂ZnS, ITO (indium tin oxide), CeO₂Or Ta₂O₃. In various embodiments, the second

dielectric region

40a or 40b may include a dielectric material having a refractive index greater than 1.65 and less than or equal to 2.5. E.g. of one or more dielectric materials in the second dielectric region 40a or 40bThe refractive index can be greater than or equal to 1.65 and less than or equal to 1.75, greater than or equal to 1.75 and less than or equal to 1.85, greater than or equal to 1.85 and less than or equal to 1.95, greater than or equal to 1.95 and less than or equal to 2.05, greater than or equal to 2.0 and less than or equal to 2.2, greater than or equal to 2.1 and less than or equal to 2.3, greater than or equal to 2.25 and less than or equal to 2.5, or any value within any range/subrange defined by these values. In some embodiments, other values outside of these ranges are also possible. In various implementations, the refractive index of one or more materials of second

dielectric region

40a or 40b may be greater than the refractive index of one or more materials of

dielectric region

30a or 30 b. The thickness of the second

dielectric region

40a or 40b may be between 75nm and 700 nm. For example, the thickness of the second

dielectric region

40a or 40b can be greater than or equal to 75nm and less than or equal to 100nm, greater than or equal to 100nm and less than or equal to 150nm, greater than or equal to 150nm and less than or equal to 200nm, greater than or equal to 200nm and less than or equal to 250nm, greater than or equal to 300nm and less than or equal to 350nm, greater than or equal to 400nm and less than or equal to 450nm, greater than or equal to 450nm and less than or equal to 500nm, greater than or equal to about 500nm and less than or equal to 650nm, greater than or equal to 650nm and less than or equal to 700nm, or any value in any range/subrange defined by these values. The second

dielectric region

40a or 40b may be disposed to cover at least 50% of an outer surface of the

metal layer

35a or 35 b. For example, the second

dielectric region

40a or 40b may be disposed to cover at least 80%, at least 90%, at least 95%, or 100% of the outer surface of the

metal layer

35a or 35b, or any value in the ranges/subranges defined by these values.

The reflected color and/or transmitted color of the

optical structure

70a or 70b comprising the second

dielectric region

40a or 40b surrounding the metal coated

dielectric region

30a or 30b may be different from the reflected color and/or transmitted color of the

optical structure

70a or 70b comprising only the metal coated

dielectric region

30a or 30 b. For example, the reflected color and/or transmitted color of

optical structure

70a or 70b including second

dielectric region

40a or 40b surrounding metal coated

dielectric region

30a or 30b may be more vivid than the reflected color and/or transmitted color of

optical structure

70a or 70b including metal coated

dielectric region

30a or 30b without second

dielectric region

40a or 40b of a material having a suitable thickness and/or a suitable refractive index. The shape of the transmission and/or reflection peak, the location of the maximum of the transmission and/or reflection peak, and/or the width of the transmission and/or reflection peak (e.g., full width at half maximum (FWHM)) of the

optical structure

70a or 70b comprising the second

dielectric region

40a or 40b surrounding the metal-coated

dielectric region

30a or 30b may be different from the shape of the transmission and/or reflection peak, the location of the maximum of the transmission and/or reflection peak, and/or the width of the transmission and/or reflection peak of the

optical structure

70a or 70b comprising the metal-coated

dielectric region

30a or 30b without the second

dielectric region

40a or 40b having a suitable thickness and/or material having a suitable refractive index. For example, the width of one or more of the reflection peaks of the

optical structure

70a or 70b comprising the second

dielectric region

40a or 40b surrounding the metal-coated

dielectric region

30a or 30b may be wider than the width of the corresponding reflection peak of the

optical structure

70a or 70b comprising the metal-coated

dielectric region

30a or 30b without the second

dielectric region

40a or 40b having a material of suitable thickness and/or suitable refractive index. As another example, in some implementations, the width (e.g., FWHM) of one or more of the reflection peaks of the

optical structure

70a or 70b including the second

dielectric region

40a or 40b surrounding the metal-coated

dielectric region

30a or 30b can be greater than or equal to about 50nm and less than or equal to about 300 nm.

Various embodiments of the

optical structure

70a or 70b including the second

dielectric region

40a or 40b surrounding the metal-coated

dielectric region

30a or 30b can have a reflection spectrum with one or more reflection peaks having a width (e.g., FWHM) greater than or equal to about 10nm, greater than or equal to about 20nm, greater than or equal to about 30n, greater than or equal to about 40nm, greater than or equal to about 50nm, greater than or equal to about 60nm, greater than or equal to about 70nm, greater than or equal to about 100nm, greater than or equal to about 200nm, less than or equal to about 300nm, less than or equal to about 250nm, or any value in the ranges/subranges defined by these values. Various implementations of the

optical structure

70a or 70b including the second

dielectric region

40a or 40b surrounding the metal-coated

dielectric region

30a or 30b may have a higher reflectivity or reflectance at one or more wavelengths in the visible spectrum as compared to the reflectivity or reflectance at the one or more wavelengths in the visible spectrum of the

optical structure

70a or 70b including the metal-coated

dielectric region

30a or 30b without the second

dielectric region

40a or 40b having a suitable thickness and/or material having a suitable refractive index.

Various embodiments of the

optical structure

70a or 70b including the second

dielectric region

40a or 40b surrounding the metal-coated

dielectric region

30a or 30b may have a transmission spectrum with one or more transmission peaks having a width (e.g., FWHM) greater than or equal to about 10nm, greater than or equal to about 20nm, greater than or equal to about 30nm, greater than or equal to about 40nm, greater than or equal to about 50nm, greater than or equal to about 60nm, greater than or equal to about 70nm, greater than or equal to about 100nm, greater than or equal to about 200nm, less than or equal to about 300nm, less than or equal to about 250nm, or any value in the ranges/subranges defined by these values.

optical structure

70a or 70b comprising the second

dielectric region

40a or 40b surrounding the metal-coated

dielectric region

30a or 30b may have a high reflectivity or reflectance. For example, the reflectance or reflectance of the one or more reflection peaks may be greater than or equal to 30%, greater than or equal to 40%, greater than or equal to 50%, greater than or equal to 55%, greater than or equal to 60%, greater than or equal to 65%, greater than or equal to 70%, greater than or equal to 75%, greater than or equal to 80%, greater than or equal to 85%, greater than or equal to 90%, greater than or equal to 95%, and less than or equal to 100%, or a value in any range/subrange defined by these values.

optical structure

70a or 70b including the second

dielectric region

40a or 40b surrounding the metal-coated

dielectric region

30a or 30b may have a high transmittance or transmittance. For example, the transmittance or transmittance of the one or more transmission peaks may be greater than or equal to 30%, greater than or equal to 40%, greater than or equal to 50%, greater than or equal to 55%, greater than or equal to 60%, greater than or equal to 65%, greater than or equal to 70%, greater than or equal to 75%, greater than or equal to 80%, greater than or equal to 85%, greater than or equal to 90%, greater than or equal to 95%, and less than or equal to 100%, or a value in any range/subrange defined by these values.

Furthermore, when the

optical structure

70a or 70b is configured as a pigment, the second

dielectric region

40a or 40b may advantageously insulate the

metal layer

35a or 35b from the ink varnish.

In some implementations, the second

dielectric region

40a or 40b can be disposed around the metal-coated

dielectric material

30a or 30b using a sol-gel process. For example, the metal coated

dielectric material

30a or 30b may be formed using a sol gel process involving hydrolysis of titanium (IV) isopropoxide with a composition comprising titanium dioxide (TiO)₂) Is coated with the dielectric material of (1). As another example, a precursor comprising the

dielectric material

40a or 40b is transformed by a series of hydrolysis and polymerization reactions to form a colloidal suspension (or "sol"). In some implementations, the colloidal suspension of dielectric material comprising the second

dielectric region

40a or 40b can be disposed on the metal-coated first

dielectric region

30a or 30b by coating, gelling, or precipitation. The metal coated first

dielectric region

30a or 30b comprising the colloidal suspension of dielectric material including the second

dielectric region

40a or 40b can be heated or dried to obtain the metal coated first

dielectric region

30a or 30b coated with the second

dielectric region

40a or 40 b. In some implementations, one or more materials of the second

dielectric region

40a or 40b can be disposed around the metal-coated first

dielectric region

30a or 30b using a deposition method (e.g., such as a chemical vapor deposition method, e-beam, sputtering). In some embodiments, various deposition methods may be combined with vibrating the metal-coated first

dielectric region

30a or 30 b.

As discussed above, various embodiments of the

optical structure

10, 70a, or 70b are configured to partially reflect light and partially transmit light. In various embodiments, the reflectivity or reflectance of the

optical structure

10, 70a, or 70b at one or more wavelengths in the visible spectrum may be greater than or equal to 10%, greater than or equal to 20%, greater than or equal to 30%, greater than or equal to 40%, greater than or equal to 50%, greater than or equal to 60%, greater than or equal to 70%, greater than or equal to 80%, greater than or equal to 90%, greater than or equal to 95%, and/or less than or equal to 100%, or any value in any range/subrange defined by these values. In various embodiments, the transmittance or transmissivity of the

optical structure

10, 70a, or 70b at one or more wavelengths in the visible spectrum may be greater than or equal to 10%, greater than or equal to 20%, greater than or equal to 30%, greater than or equal to 40%, greater than or equal to 50%, greater than or equal to 60%, greater than or equal to 70%, greater than or equal to 80%, greater than or equal to 90%, greater than or equal to 95%, and/or less than or equal to 100%, or any value in any range/subrange defined by these values. In various implementations, the reflectance or reflectance of the

optical structure

10, 70a, or 70b at one or more first set of wavelengths may be approximately equal to the transmittance or transmittance of the

optical structure

10, 70a, or 70b at one or more second set of wavelengths different from the first set of wavelengths.

The

optical structures

10, 70a, or 70b can have a size, for example, greater than or equal to about 1 micron and less than or equal to about 50 microns, such as a lateral dimension, area, length, or width of the optical structure (e.g., a length, width, or area of a major surface of the optical structure). For example, the size of the

optical structures

10, 70a, or 70b can be greater than or equal to about 1 micron and less than or equal to 10 microns, greater than or equal to 2 microns and less than or equal to 12 microns, greater than or equal to 3 microns and less than or equal to 15 microns, greater than or equal to 4 microns and less than or equal to 18 microns, greater than or equal to 5 microns and less than or equal to 20 microns, greater than or equal to 10 microns and less than or equal to 20 microns, greater than or equal to 15 microns and less than or equal to 25 microns, greater than or equal to 20 microns and less than or equal to about 30 microns, greater than or equal to 25 microns and less than or equal to 35 microns, greater than or equal to 30 microns and less than or equal to 40 microns, greater than or equal to 35 microns and less than or equal to 45 microns, greater than or equal to 40 microns and less than or equal to 50 microns, or a value in any range/subrange defined by these values.

The

optical structures

10, 70a, or 70b can have a size, for example, greater than or equal to about 1 micron and less than or equal to about 50 microns, e.g., a lateral dimension, area, length, or width of the optical structure (e.g., a length, width, or area of a major surface of the optical structure), can be between 0.1 micron and 2.0 microns. For example, the thickness of the

optical structure

10, 70a, or 70b has a value such as, for example, greater than or equal to 0.1 micron and less than or equal to 0.3 micron, greater than or equal to 0.2 micron and less than or equal to 0.5 micron, greater than or equal to 0.3 micron and less than or equal to 0.6 micron, greater than or equal to 0.4 micron and less than or equal to 0.7 micron, greater than or equal to 0.5 micron and less than or equal to 0.8 micron, greater than or equal to 0.6 micron and less than or equal to 0.9 micron, greater than or equal to 0.7 micron and less than or equal to 1.0 micron, greater than or equal to 1.0 micron and less than or equal to 1.2 micron, greater than or equal to 1.2 micron and less than or equal to 1.5 micron, greater than or equal to 1.5 micron and less than or equal to 2.0 micron, or any range/subrange defined by these values, such as a lateral dimension, an area, a length, or width (e.g., a length of a major surface of the optical structure, Width or area).

One or more of the

optical structures

10, 70a, or 70b discussed above may be incorporated with or in a document (e.g., a banknote), package, product, or other item. An optical product (e.g., film, wire, ply, foil, pigment, or ink) including one or more of the above-discussed

optical structures

10, 70a, or 70b may be incorporated with or in a document (e.g., a banknote or other document) to verify the authenticity of the document, packaging material, or the like. For example, the

optical structure

70a or 70b may be configured as an ink or pigment disposed on a substrate comprising at least one of a polymer, plastic, paper, or fabric. In some embodiments, the substrate may be flexible. The substrate comprising the ink or pigment or pigments comprising the

optical structures

70a or 70b may be cut or diced to obtain a wire or foil. The plurality of

optical structures

10, 70a, or 70b discussed above may be incorporated into a particular optical product (e.g., ink, pigment, thread, filament, paper, security ink, security pigment, security thread, security filament, security paper, etc.). The shape, size, and/or aspect ratio of the plurality of

optical structures

10, 70a, or 70b discussed above incorporated in a particular optical product (e.g., ink, pigment, thread, filament, paper, security ink, security pigment, security thread, security filament, security paper, etc.) may vary. Thus, a particular optical product (e.g., ink, pigment, thread, filament, paper, security ink, security pigment, security thread, security filament, security paper, etc.) may include

optical structures

10, 70a, or 70b having a different distribution of shapes, sizes, and/or aspect ratios of the optical structures. For example, a particular optical product (e.g., ink, pigment, thread, filament, paper, security ink, security pigment, security thread, security filament, security paper, etc.) may include

optical structures

10, 70a, or 70b having a size distributed around one or more average sizes. As another example, a particular optical product (e.g., ink, pigment, thread, filament, paper, security ink, security pigment, security thread, security filament, security paper, etc.) may include

optical structures

10, 70a, or 70b having aspect ratios distributed around one or more aspect ratios.

Fig. 10 shows, for example, a banknote 80 including a laminate film 83. The laminate film 83 includes the

optical structure

10, 70a, or 70 b. The laminate film 83 may be fabricated by disposing the

optical structure

10, 70a, or 70b over a base or support layer or substrate, such as a polymeric base layer (e.g., polyester film). The

optical structure

10, 70a, or 70b may be disposed over the polymeric base layer by various methods including, but not limited to, coating methods, vacuum deposition on the surface of the polymeric base layer, and the like. The

optical structure

10, 70a, or 70b may be disposed over a first side of a surface of a polymer base layer (e.g., a polyester film). The laminated film 83 may be adhered to the "paper" (e.g., cellulose, cotton/linen, polymer or fabric) 81 of the banknote 80, for example, by a transparent and/or optically clear adhesive. In each case, a second surface of the polymeric base layer, opposite the first surface of the base layer, is disposed closer to the banknote paper 81 making up the banknote and may be in contact with the adhesive. In some cases, the adhesive may be a two-component adhesive with one component disposed on the currency paper and the other component disposed on a second surface of the polymeric substrate layer opposite the first surface of the substrate layer on which the

optical structure

10, 70a, or 70b is disposed. The bill 80 and the laminated film 83 may be put together for bonding. The laminate film 83 may also be attached to the paper money 80 using a crosslinked thermosetting adhesive. A transparent protective barrier coating 82 (e.g., a UV curable cross-linked resin) may be disposed over the laminate film 83. The protective barrier coating 82 may extend over the edges of the laminating film 83 onto the paper (e.g., fabric) 81 of the banknote. The protective barrier coating 82 may be configured to protect the laminated film 83 from corrosion, abrasion, and liquids that may typically come into contact with the banknote 80 without sacrificing the optical effect provided by the laminated film 83. The optical structure 10 may be disposed facing the protective barrier coating 82 or an adhesive layer between the laminating film 83 and the "paper" 81.

In some embodiments,

optical structures

10, 70a, or 70b may be configured as a line (e.g., a windowed line) rather than a laminated film. The windowed thread can be manufactured by various methods. For example, the in-line weave may be into the paper and to the surface of the paper during the papermaking process. As another example, the windowed thread may be disposed within the paper itself such that portions of the thread do not reach the surface of the banknote. As yet another example, open space within the paper may be provided in an area of the paper that includes the thread.

The thread may be made by cutting a strip of the optical structure 10 (e.g., a web, sheet, or substrate layer on which the layers comprising the optical structure 10 are formed) and passing the strip through a bath of UV curable resin. The rate at which the strip passes through the bath of UV curable resin can be controlled to uniformly coat the sides and edges of the strip. The tape coated with the UV curable resin may be cured to obtain a thread. The resulting thread including optical structure 10 may be inserted (e.g., woven) into a banknote. In some embodiments, any edges of the lines (due to hot embossing or chatter from any cutting operation) (e.g., jagged or uneven edges of the lines) may be hidden from the viewer by printing an opaque border around the hot embossed patch. Another way of affixing the

optical structure

10, 70a or 70b to a banknote can include die cutting a portion of the optical structure (e.g., a web, sheet or substrate layer on which the layer comprising the

optical structure

10, 70a or 70b is formed) and applying the portion to the banknote using an adhesive. Various implementations of the examples of optical structures described above may be configured as threads, hot stamps, or plies and incorporated with or in documents (e.g., banknotes), packages, products, or other items.

Without loss of generality, the

optical structure

10, 70a, or 70b or a material (e.g., ink, paint or pigment, varnish) comprising the

optical structure

10, 70a, or 70b may be disposed on a substrate comprising at least one of a polymer, plastic, paper, or fabric. The substrate comprising

optical structure

10, 70a, or 70b or the material comprising

optical structure

10, 70a, or 70b may be cut or diced into smaller portions having various shapes and/or sizes. The smaller portion may be disposed on or inserted into a substrate (e.g., banknotes, paper, packaging material, fabric, etc.) or inserted onto the substrate using various methods. For example, the smaller portion may be configured as a strip or wire that may be woven into the substrate. As another example, the smaller portion may be configured as a foil that may be hot stamped on the substrate. As yet another example, the smaller portion may be laminated to the substrate using an adhesive.

Fig. 11A depicts a banknote 90a, the banknote 90a having two transparent windows 91A and 92a inserted into or attached to the paper (e.g., fabric) of the banknote. Each window includes an

optical structure

10, 70a or 70 b. In some implementations, the reflection spectrum and/or transmission spectrum of the optical structure 10 of window 91a can be configured to be different from the reflection spectrum and/or transmission spectrum of the

optical structure

10, 70a, or 70b of window 92 a. Thus, a person viewing banknote 90a will perceive a first reflected color when viewing window 91a along a viewing direction (e.g., normal to the surface of banknote 90 a) and a second reflected color that is not used for the first reflected color when viewing window 92a along the viewing direction. The person may also perceive a third transmitted color different from the first reflected color when viewed through window 91a along the viewing direction. Further, the person may perceive a fourth transmitted color different from the first, second, and third colors when viewed through window 92a along the viewing direction. Furthermore, after folding the note 90a over itself such that the two

windows

91a and 92a are at least partially aligned with respect to each other, the person will perceive different colors different from the first, second, third and/or fourth colors in the reflective mode and the transmissive mode when viewing the note 90a along the viewing direction. For example, after folding the banknote 90a over itself such that the two

windows

91a and 92a are at least partially aligned relative to each other, the person will perceive a reflected color (which is a combination of the effects of the reflectance or reflectance spectra of the two

windows

91a and 92 a) and a transmitted color (which is a combination of the effects of the transmission spectra of the two

windows

91a and 92 a). Furthermore, the person may perceive color shifts of the various colors seen in the reflective mode and the transmissive mode as the viewing angle changes. The amount of color shift may be different for different windows and combinations of two windows.

Fig. 11B depicts an implementation of a security device 90B (e.g., a banknote), the security device 90B comprising two windows 91B and 92B (a first window and a second window) inserted into a surface of the security device 90B or attached to a surface of the security device 90B. The two

windows

91b and 92b at least partially overlap in an overlap region 93 b. The two

windows

91b and 92b are transparent and comprise the

optical structure

10, 70a or 70 b. The configuration (e.g., thickness or other design parameter) of

optical structures

10, 70a, or 70b in

respective windows

91a and 91b may be such that the reflectance spectrum and/or transmission spectrum of

optical structure

10, 70a, or 70b of window 91b is different from the reflectance spectrum and/or transmission spectrum of optical structure 10 of window 92 b.

Thus, a person viewing security device 90b along a viewing direction (e.g., normal to the surface of security device 90 b) will: (i) a first reflected color is perceived when viewing the portion of window 91b that does not overlap window 92 b; (ii) a second reflected color different from the first color is perceived when viewing the portion of window 92b that does not overlap window 91 b; and (iii) a third, second reflected color is perceived when viewing the overlap region 93b, which is a combination of the effects of the reflectivity or reflectance spectra of the two

windows

91b and 92 b.

A person viewing security device 90b along a viewing direction (e.g., normal to the surface of security device 90 b) would: (i) a fourth transmitted color different from the first color is perceived when viewed through the portion of window 91b that does not overlap window 92 b; (ii) a fifth transmitted color different from the second color and the fourth color is perceived when viewed through the portion of window 92b that does not overlap window 91 b; and (iii) a sixth transmitted color is perceived when viewed through the overlap region 93b, which is a combination of the effects of the transmission spectra of the two

windows

91b and 92 b.

Furthermore, in various embodiments, a person viewing security device 90b may perceive color shifts of various colors seen in the reflective mode and transmissive mode as the viewing angle changes. The amount of color shift may be different for different windows.

Although the two windows 91B and 92B are shown as partially overlapping in fig. 11B, the two windows 91B and 92B may completely overlap. Various embodiments of the security device 90b may include two or more different pigments. The two or more different pigments may include optical structures 10. The respective optical structure of one of the two or more different pigments may have different reflectivity and transmittance characteristics than the respective optical structure of the other of the two or more different pigments. Two or more different pigments may partially or completely overlap each other. As discussed above, the color perceived by a person viewing overlapping regions of two or more different pigments may depend on a combination of the effects of the reflection/transmission spectra of the different optical structures of the two or more different pigments. Some implementations of the security device 90b may include two or more at least partially overlapping foils, films, threads, or plies that include different optical structures. The color perceived by a person viewing an overlapping region of two or more at least partially overlapping foils, films, lines or plies may depend on a combination of the effects of the reflection/transmission spectra of the different optical structures of the two or more foils, films, lines or plies.

Fig. 12 illustrates a side view of an object 100 with a security device, the object 100 comprising a body 103 of the object and a layer 102 comprising an

optical structure

10, 70a or 70 b. The object may be a banknote. The main body may include paper constituting the paper money. The layer 102 may be a ply, a line, or indicia. When the layer 102 is configured as a marker, an adhesive (e.g., a varnish) may be applied to the body 103 and the layer 102 may be adhered to the adhesive of the body 103 using a polymeric adhesive. Alternatively, the adhesive may be applied to the layer 102 prior to affixing to the body 103. When the layer 102 is configured as a ply, a polymer may be used to adhere the layer 102 to the body 103.

The layer 102 may be adhered to the body 103 using an adhesive, such as, for example, an optically clear adhesive and/or a cross-linked thermoset adhesive. The security device 100 further comprises a layer 101, the layer 101 comprising a message composed using words, symbols, numbers or any combination thereof, the layer 101 being disposed on the side of the body (e.g. paper/fabric) 103 of an object (e.g. banknote) opposite to the side where the layer 102 is located, as shown in fig. 12. Alternatively, layer 101 may be disposed between body (e.g., paper/fabric) 103 and layer 102 or disposed over layer 102. Layer 101 may comprise, for example, a dye, pigment, or phosphorescent material having the same chromatic characteristics as the color reflected or transmitted by optical structure 10 when viewed along a direction normal to the surface of layer 102. Thus, when the security device 100 is viewed along a direction normal to the surface of the layer 102, the message is not visible (or hidden) to an observer. However, when the security device 100 is tilted such that the viewing angle changes, the color reflected by the optical structure 10 and/or transmitted through the optical structure 10 changes such that the message is visible to the observer. In certain cases, the layer 101 comprising messages printed with phosphorescent material may be made visible when illuminated by UV. The resulting color of the phosphorescent material may be a combined color of fluorescent and bi-chromatic colors.

Fig. 13 shows the effect of changing the viewing angle in the transmission of the security device 100 from 0 degrees to about 45 degrees. When the viewing angle is 0 degrees, the message comprising a combination of numbers, letters or symbols is not visible in the transmissive mode because the color of the letters is the same as the color of the optical structure in the transmissive mode (e.g., orange). However, as the viewing angle increases, the color of the optical structure shifts in the transmissive mode. For example, as the viewing angle increases, the message 203 becomes visible as the color of the optical structure in the transmissive mode shifts from orange to yellow. The color of the message is of sufficient contrast relative to the transmitted color of the optical structure 10 so as to be visible to an observer.

In other embodiments, the security device 100 may be configured to operate in reverse to that described above such that, for example, messages are visible at normal incidence and not visible when the security device is tilted. Other variations are possible.

As described above, the

optical structure

10, 70a, or 70b may be used in different forms, such as a ply, foil, film, hot stamp, wire, pigment, ink, or paint. In some embodiments, the ply, foil, film or wire may include a pigment, ink or coating that includes the

optical structure

10, 70a or 70 b. The ply may be adhered to the document, product or packaging using an adhesive. The thread may be threaded or woven through an opening in the document, for example. The foil may be hot stamped onto the document, product or package. The pigment, ink, or coating may be deposited on the document, product, or packaging or the material (e.g., paper, paperboard, or fabric) used to form the document, product, or packaging. For example, a document, product, or package may be exposed to (e.g., contacted with) a pigment, ink, or paint to color the document, product, or package in a process similar to that used for non-color shifting pigments, dyes, paints, and inks.

A plurality of

optical structures

10, 70a, or 70b, such as described herein, collected together as pigments (as well as inks and coatings) may have optical properties similar to the

optical structures

10, 70a, or 70b configured as films/plies. As described above, the

optical structures

10, 70a, or 70b that are brought together to form the pigment can exhibit a collection of flakes or discrete pieces having the same optical properties as the overall optical film from which the flakes are made. An additional advantage of

optical structures

10, 70a, or 70b configured as pigments is that the colors can be blended according to desired specifications. The color of the optical structure 10 may be designed by using computer software to calculate the thickness of the various layers of the

optical structure

10, 70a, or 70b that provide the desired reflection and/or transmission characteristics. The

optical structures

10, 70a, or 70b that can provide a particular color can be designed using computer software and then manufactured. Furthermore, different color-shifting

optical structures

10, 70a, or 70b that produce different colors may be included together and/or color-shifting optical structures such as described herein may be combined with non-color-shifting pigments or dyes to produce different colors.

The

optical structure

10, 70a, or 70b can be fabricated using various methods including, but not limited to, vacuum deposition, coating methods, and the like. One method of making the optical structure 10 described herein uses a vacuum coater that employs batch coating or roll coating. In one method of making the optical structure 10, a first transparent high refractive index layer (e.g., layer 12 or layer 16 of FIG. 1) is deposited onto a carrier or base layer (e.g., a sheet or web or other substrate). The carrier, web, base layer, or substrate may comprise a material such as, for example, polyester or polyester having release properties such that the optical structure may be readily separated from the web or base layer. A release layer between the base layer and a plurality of other optical layers forming the optical structure may be used to allow the optical layer comprising the optical structure to be separated from the base layer or the web. A first metal layer (e.g., layer 13 or layer 15), a transparent dielectric layer comprising a high or low refractive index material (e.g., layer 14), a second metal layer (e.g., layer 15 or layer 13), and a second transparent high refractive index layer (e.g., layer 16 or layer 12) are sequentially deposited over the first transparent high refractive index layer (e.g., layer 12 or layer 16 of fig. 1). In some embodiments, the different layers may be deposited sequentially. However, in other embodiments, one or more interposers may be disposed between any of the first metal layer, the transparent dielectric layer comprising high or low refractive index material, the second metal layer, and the second transparent high refractive index layer. As an example, in some cases, the transparent high refractive index layer and the dielectric layer may be deposited using an electron gun, while the first metal layer and the second metal layer may be deposited using an electron gun or sputtering.

Some materials (such as ZnS or MgF2) may be evaporated from a resistive source. In the example where the transparent dielectric layer comprising a high or low refractive index material comprises a polymer, a process known as PML (polymer multilayer) as described in US 5,877,895 may be used. The entire disclosure of US 5,877,895 is incorporated herein by reference.

The invention described herein describes a wide variety of structures and methods, but should not be construed as limited to the specific structures or methods described. For example, although many of the example optical structures 10 are symmetrical, asymmetrical structures are possible. For example, dielectric layers having different characteristics (e.g., thickness or material) may be used on opposite sides of the structure or alternatively may have dielectric layers only on the sides of the metal layer pair, rather than having a pair of similar or identical dielectric layers sandwiching the metal layer pair. Similarly, the metal layers need not be identical and may have different characteristics (e.g., different thicknesses or materials). An interposer, as described above, may also be included. One or more such interposers may be included such that the optical structure is asymmetric. For example, an interposer may be included between dielectric layer 12 and metal layer 13, rather than between metal layer 15 and dielectric layer 16, or vice versa. Similarly, an interposer may be included between metal layer 13 and dielectric layer 14 rather than between dielectric layer 14 and metal layer 15 or vice versa. Similarly, interposers having different characteristics (e.g., materials or thicknesses) may be included on different sides of the optical structure 10. Alternatively, more intervening layers may be included on one side of the optical structure 10 than on the other side of the optical structure. For example, metal layer 13 and/or metal layer 15 may comprise a metal sublayer. In some implementations, the metal layer 13 and/or the metal layer 15 may include a first metal (e.g., silver) facing the high refractive index

transparent layer

12 or 16 and a second metal (e.g., gold) facing the dielectric layer 14.

Likewise, although this disclosure describes the application of the structures and methods described herein to include security applications (e.g., to resist the successful use of counterfeit currency, documents, and products), this disclosure should not be considered limited to that particular application. Alternatively or additionally, such features may be used, for example, to provide aesthetic effects, creating attractive or attractive features on a product or package for marketing and advertising or other reasons.

The dimensions (e.g., thickness, length, width) of the various embodiments described herein may be outside of the different ranges provided in the present disclosure. The values of the refractive indices for the various materials described herein may be outside of the different ranges provided in the present disclosure. The values of reflectivity and/or transmissivity for different structures may be outside of the different ranges provided herein. The values for the spectral widths and peak positions of the reflection spectrum and transmission spectrum may be outside the different ranges provided herein.

Various embodiments of the present invention have been described herein. While the invention has been described with reference to these specific embodiments, the description is intended to be illustrative of the invention and is not intended to be limiting. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention.

Claims

1. An optical structure, comprising:

a second transparent dielectric layer disposed over the first metal layer;

2. The optical structure of claim 1 wherein the second transparent dielectric layer has a refractive index of less than 1.65.

3. The optical structure of claim 1, wherein the second transparent dielectric layer has a refractive index greater than or equal to 1.65.

4. The optical structure of claim 1, having a transmission peak comprising:

a maximum transmission of greater than 50%; and

a spectral bandwidth defined by the full width of the transmission peak of the 50% maximum transmission,

wherein the maximum transmittance is at least 50%, and

wherein the spectral bandwidth of the transmission peak is greater than 2 nm.

5. The optical structure of claim 4, wherein the spectral bandwidth of the transmission peak is greater than or equal to about 10nm and less than or equal to about 200 nm.

6. The optical structure of claim 4, wherein the maximum transmission is at a wavelength between about 400nm and about 700 nm.

7. The optical structure of claim 4, further comprising a reflection peak comprising:

a maximum reflectance; and

a spectral bandwidth defined by the full width of the reflection peak of said 50% maximum reflectance,

wherein the maximum reflectance is at least 50%, and

wherein the spectral bandwidth of the reflection peak is greater than 2 nm.

8. The optical structure of claim 7, wherein the spectral bandwidth of the reflection peak is greater than or equal to about 10nm and less than or equal to about 200 nm.

9. The optical structure of claim 7, wherein the maximum reflectance is at a wavelength between about 400nm and about 700 nm.

10. The optical structure of claim 7, wherein the maximum transmittance is at a first wavelength, and wherein the maximum reflectance is at a second wavelength different from the first wavelength.

11. The optical structure of claim 1, configured to display a first color when viewed by a typical human eye along a direction normal to a surface of the optical structure in a reflective mode and a second color different from the first color when viewed by a typical human eye along a direction normal to a surface of the optical structure in a transmissive mode.

12. The optical structure of claim 11, wherein the first color shifts to a third color when viewed by the average human eye in a direction angled away from a normal to a surface of the optical structure in a reflective mode.

13. The optical structure of claim 11, wherein the second color shifts to a fourth color when viewed by the average human eye in a direction angled away from a normal to a surface of the optical structure in a transmissive mode.

14. The optical structure of claim 1, wherein the first or second metal layer has a thickness greater than or equal to about 5nm and less than or equal to about 35 nm.

15. The optical structure of claim 1, wherein the second transparent dielectric layer has a thickness greater than or equal to about 100nm and less than or equal to about 2 microns.

16. The optical structure of claim 1, wherein first transparent dielectric layer or the third transparent dielectric layer has a thickness greater than or equal to about 100nm and less than or equal to about 500 nm.

17. The optical structure of claim 1, further comprising an encapsulation layer comprising silicon dioxide.

18. The optical structure of claim 17 wherein the silica is bonded to a silane coupling agent.

19. The optical structure of claim 18, wherein the silane coupling agent is configured to bond to an ink medium or a coating medium.

20. The optical structure of claim 1, wherein the first or second metal layer comprises at least one of aluminum, silver, gold, silver alloy, or gold alloy.

21. The optical structure of claim 1 wherein the second transparent dielectric layer comprises a material having a refractive index less than 1.65, greater than 1.65, or equal to 1.65.

22. The optical structure of claim 1 wherein the second transparent dielectric layer comprises SiO₂、MgF₂Or a polymer.

23. The optical structure of claim 1, wherein the first or third transparent dielectric layer comprises zinc oxide (ZnO), zinc sulfide (ZnS), zirconium dioxide (ZrO), or a combination thereof₂) Titanium dioxide (TiO)₂) Tantalum pentoxide (Ta)₂O₅) Cerium oxide (CeO)₂) Yttrium oxide (Y)₂O₃) Indium oxide (In)₂O₃) Tin oxide (SnO)₂) Indium Tin Oxide (ITO) and tungsten trioxide (WO)₃) Or a combination thereof.

24. The optical structure of claim 1, wherein the first or second metal layer has a thickness greater than or equal to about 5nm or less than or equal to about 35 nm.

25. The optical structure of claim 1, wherein the second transparent dielectric layer has a thickness greater than or equal to about 100nm or less than or equal to about 700 nm.

26. The optical structure of claim 1, wherein the first or third transparent dielectric layer has a thickness greater than or equal to about 100nm or less than or equal to about 500 nm.

27. The optical structure of claim 1, configured as a film, pigment, coating, or ink.

28. The optical structure of claim 1, further comprising a base layer configured to support the first dielectric layer, wherein the optical structure is configured as a film.

29. The optical structure of claim 28 wherein the base layer is flexible.

30. The optical structure of claim 28 wherein the base layer comprises a polymer.

31. The optical structure of claim 28 wherein the film is surrounded by a protective barrier.

32. The optical structure of claim 31 wherein the protective barrier comprises a UV curable resin.

33. The optical structure of claim 1, further comprising an encapsulation layer, wherein the optical structure is configured as a pigment, a coating, or an ink.

34. The optical structure of claim 33 wherein the encapsulation layer comprises silicon dioxide (SiO)₂)。

35. The optical structure of claim 33, further comprising a plurality of silica spheres embedded in the encapsulation layer.

36. The optical structure of claim 35 wherein the size of some of the plurality of silica spheres is different from the size of others of the plurality of silica spheres.

37. The optical structure of claim 33, wherein the encapsulation layer is chemically attached to a silane coupling agent comprising a reactive group configured to chemically bond with an ink medium or a coating medium.

38. The optical structure of claim 37 wherein the ink medium or the coating medium comprises a material selected from the group consisting of: melamine acrylates, urethanes, polyesters, vinyl resins, acrylates, methacrylates, ABS resins, epoxy resins, styrenes, and alkyd-based formulations, and mixtures thereof.

39. The optical structure of claim 37 wherein the ink medium or the coating medium comprises a resin or a polymer.

40. A banknote or document comprising the optical structure of claim 1.

41. The banknote or document according to claim 40, wherein said optical structure is configured to be attached to a ply of said banknote or document.

42. The banknote or document according to claim 40, wherein said optical structure is configured as a security thread inserted into said banknote or document.

43. The banknote or document according to claim 40, wherein said optical structure is configured as a tag attached to said banknote or document.

44. The banknote or document according to claim 40, further comprising a window, wherein said optical structure is incorporated in said window.

45. A document having a security feature, comprising:

a body of the document; and

an optical structure, comprising:

a second transparent dielectric layer disposed over the first metal layer;

46. The security document of claim 45, further comprising a second optical structure, the second optical structure comprising:

a fifth transparent dielectric layer disposed over the third metal layer;

a sixth transparent dielectric layer disposed over the fourth metal layer having a refractive index greater than or equal to 1.65,

47. The security document of claim 46, wherein the optical structure or the second optical structure is configured as a film that is attached to the body of the document.

48. The security document of claim 46, wherein the optical structure or the second optical structure is configured as a wire inserted into the body of the document.

49. The security document of claim 46, wherein the optical structure or the second optical structure is configured as a ply disposed over a body of the document.

50. The security document of claim 46, wherein the optical structure or the second optical structure is configured to contact an ink, dye, or paint of the body of the document.

51. The security document of claim 46, further comprising a first window comprising the optical structure and a second window comprising the second optical structure.

52. The security document of claim 45, wherein the optical structure is configured as a two-color ink, a two-color pigment, or a two-color paint configured to produce a first color at a first viewing angle and a second color at a second viewing angle.

53. The security document of claim 52, wherein the document is printed with the bi-color ink, the bi-color pigment, or the bi-color paint.

54. The security document of claim 53, wherein the bi-color ink, the bi-color pigment, or the bi-color coating is disposed above, below, or mixed with a non-bi-color ink, pigment, or coating configured to produce the first color at the first and second viewing angles.

55. The security document of claim 54, wherein the non-bi-color, ink pigment, or paint forms a word, image, number, or symbol.

56. The security document of claim 55, wherein the text, the image, the number, or the symbol are not visible at the first viewing angle and are visible at the second viewing angle.

57. The security document of claim 55, wherein the text, the image, the number, or the symbol are not visible at the second viewing angle and are visible at the first viewing angle.

58. A method of manufacturing a security feature configured to produce a first color in a reflective mode and a second color in a transmissive mode, the method comprising:

providing a base layer; and

a second transparent dielectric layer disposed over the first metal layer;

59. The method of claim 58, wherein disposing the optical structure on the base layer comprises:

coating the first transparent dielectric layer on the base layer;

depositing the first metal layer on the first transparent dielectric layer;

disposing the second transparent dielectric layer on the first metal layer;

disposing the third transparent dielectric layer on the second metal layer.

60. The method of claim 58, further comprising:

cutting a strip of the base layer having the optical structure; and

the strip was coated with a UV curable polymer to obtain a security thread.

61. The method of claim 58, further comprising:

removing the optical structure from the base layer;

attaching a silane coupling agent to the encapsulation layer; and

62. The method of claim 59, wherein disposing the second transparent dielectric layer on the first metal layer comprises depositing the second transparent dielectric layer on the first metal layer.

63. The method of claim 59, wherein disposing the third transparent dielectric layer on the second metal layer comprises depositing the third transparent dielectric layer on the second metal layer.

64. The method of claim 58, further comprising:

removing the optical structure from the base layer;

attaching a silane coupling agent to the optical structure; and

65. The method of claim 64, further comprising:

encapsulating the sheet in an encapsulation layer; and

attaching the silane coupling agent to the encapsulation layer.

66. The method of claim 58, wherein the base layer is flexible.

67. The method of claim 58, wherein the base layer comprises a mesh.

68. The method of claim 59, further comprising depositing the first metal layer on the first transparent dielectric layer using an electroless plating process.

69. The method of claim 59, further comprising depositing the second metal layer on the second transparent dielectric layer using an electroless plating process.

70. An optical structure, comprising:

a substrate;

a first optical structure over the substrate; and

a second transparent dielectric layer disposed over the first metal layer;

wherein the thickness of each layer of the first optical structure is configured to reflect a first color and transmit a second color different from the first color, and

wherein thicknesses of layers of the second optical structure are configured to reflect a third color different from the first color and transmit a fourth color different from the first color, the second color, or the third color.

71. The optical structure of claim 70 wherein the first optical structure completely overlaps the second optical structure.

72. The optical structure of claim 70, wherein the first and second optical structures are configured as films.

73. The optical structure of claim 70, wherein the first and second optical structures are configured as pigments.

74. The optical structure of claim 70 wherein the first and second optical structures are configured as plies.

75. The optical structure of claim 70, wherein the first and second optical structures are configured as a security thread.

76. A document having a security feature, comprising:

a body of the document; and

a pigment disposed on the body, the pigment comprising:

an optical structure, comprising:

a transparent dielectric layer disposed over the first metal layer; and

an encapsulation layer encapsulating the optical structure.

77. The document of claim 76, wherein the encapsulation layer comprises silicon dioxide.

78. The document of claim 76, wherein the pigment produces a first color at a first viewing angle and a second color different from the first color at a second viewing angle.

79. The document of claim 76, wherein the pigment comprises a resin configured to be chemically attached to the encapsulation layer.

80. The document of claim 76, wherein the optical structure has a thickness, and wherein a length or width of the optical structure is at least 5 times the thickness.

81. An optical structure, comprising:

a partially optically transmissive metal layer surrounding an outer surface of the dielectric region,

82. The optical structure of claim 81, further comprising a second dielectric region comprising one or more dielectric materials having a refractive index greater than about 1.65, the second dielectric region surrounding the partially optically transmissive metal layer.

83. The optical structure of any one of claims 81 to 82 wherein the partially optically transmissive metal layer covers at least 80% of the outer surface of the dielectric region.

84. The optical structure of claim 83 wherein the partially optically transmissive metal layer covers at least 90% of the outer surface of the dielectric region.

85. The optical structure of claim 83 or claim 84 wherein the partially optically transmissive metal layer covers 100% of the outer surface of the dielectric region.

86. The optical structure of claim 81 wherein the dielectric region is spherical, elliptical, or circular.

87. The optical structure of claim 81 wherein the dielectric region is a cube or rectangular cuboid.

88. The optical structure of claim 81 wherein the dielectric region comprises particles or flakes.

89. The optical structure of claim 81 wherein the partially optically transmissive metal layer comprises silver.

90. The optical structure of claim 81, wherein the partially optically transmissive metal layer has a thickness between about 3nm and about 40 nm.

91. The optical structure of claim 81 wherein the dielectric region comprises silicon dioxide or titanium dioxide.

92. The optical structure of claim 82 wherein the second dielectric layer comprises a material having an index of refraction greater than about 1.65.

93. The optical structure of claim 82 wherein the second dielectric layer comprises titanium dioxide.

94. The optical structure of claim 82 wherein the second dielectric layer covers at least 80% of the outer surface of the partially optically transmissive metal layer.

95. The optical structure of claim 82 wherein the second dielectric layer covers at least 90% of the outer surface of the partially optically transmissive metal layer.

96. The optical structure of claim 82 wherein the second dielectric layer covers at least 95% of the outer surface of the partially optically transmissive metal layer.

97. The optical structure of claim 82 wherein the second dielectric layer covers 100% of the outer surface of the partially optically transmissive metal layer.

98. Any one of claims 81 to 97The optical structure of, wherein the dielectric region comprises SiO₂。

99. The optical structure of any one of claims 81 to 97 wherein the dielectric region comprises TiO₂。

100. The optical structure of any one of claims 81 to 97, wherein the dielectric region comprises borosilicate having a high refractive index metal oxide layer thereon.

101. The optical structure of any one of claims 81 to 97 wherein the dielectric region comprises having TiO thereon₂The borosilicate of (a).

102. The optical structure of any one of claims 81 to 97, wherein the dielectric region comprises having SiO thereon₂The borosilicate of (a).

103. The optical structure of any one of claims 81 to 97 comprised in a security thread or security ink.

104. The optical structure of any one of claims 81 to 97 being included in a film.

105. The optical structure of any one of claims 81 to 97 being included in a flexible film having a flexible substrate.

106. The optical structure of any one of claims 81 to 97 comprised in a pigment, coating or ink.

107. A security document comprising the optical structure of any one of claims 81 to 97.

108. A security document comprising the optical structure of any one of claims 81 to 97, wherein the first color and the second color are complementary colors.

109. A method of manufacturing a bi-color ink or bi-color coating configured to produce a first color in a reflective mode and a second color in a transmissive mode, the method comprising:

providing a base layer; and

a first transparent dielectric layer disposed over the first metal layer; and

110. The method of claim 109, further comprising:

removing the optical structure from the base layer;

111. The method of claim 110, further comprising:

individual sheets are encapsulated in an encapsulation layer comprising a plurality of silicon dioxide spheres.

112. The method of claim 111, further comprising:

attaching a silane coupling agent to the encapsulation layer.

113. The method of any one of claims 109-111, wherein the optical structure further comprises:

114. A bi-color ink or bi-color coating configured to produce a first color in a reflective mode and a second color in a transmissive mode, the bi-color ink or bi-color coating comprising:

a base layer; and

an optical structure on the base layer, the optical structure comprising:

a first transparent dielectric layer disposed over the first metal layer; and

115. The bi-colored ink or bi-colored coating of claim 114, wherein the optical structure further comprises:

116. The bi-colored ink or bi-colored coating of any one of claims 114 to 119, further comprising an ink medium or a coating medium comprising the optical structure, wherein the optical structure has a thickness of between 100nm and 2 microns, and wherein a lateral dimension of the optical structure is between 1 micron and 20 microns.

117. A pigment, comprising:

an optical structure, comprising:

a transparent dielectric layer disposed over the first metal layer; and

118. The pigment of claim 117, further comprising an encapsulation layer encapsulating said optical structures.

119. The pigment of claim 118, wherein said encapsulation layer comprises silicon dioxide.

120. The pigment of claim 118, further comprising a resin configured to be chemically attached to said encapsulation layer.

121. The pigment of claim 117, configured to be a first color at a first viewing angle and a second color different from said first color at a second viewing angle.

122. The pigment of claim 117, wherein said optical structure has a thickness, and wherein the length or width of said optical structure is at least 5 times said thickness.

123. A document, comprising:

a main body;

the pigment of claim 117, disposed on said body.

124. A package, comprising:

a main body;

the pigment of claim 117, disposed on said body.